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Do snail shells increase the number of rounds with age?

Do snail shells increase the number of rounds with age?


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Do snail shells increase the number of rounds with snail age?


Yes. Once secreted the shell cannot increase in size, so that the growth of the body is accompanied by continuous growth of the shell, i.e. by the gradual increase in the number of the whorls.

This also means that the topmost whorls are the oldest and the aperture marks the front of the new shell.


Breeding system, shell size and age at sexual maturity affect sperm length in stylommatophoran gastropods

Sperm size and quality are key factors for fertilization success. There is increasing empirical evidence demonstrating that sperm form and function are influenced by selective pressures. Theoretical models predict that sperm competition could favour the evolution of longer sperm. In hermaphrodites, self-fertilizing species are expected to have shorter sperm than cross-fertilizing species, which use sperm stored from several mating partners for the fertilization of their eggs and thus are exposed to intense sperm competition. We tested this hypothesis by comparing original data on sperm length in 57 species of simultaneously hermaphroditic stylommatophoran gastropods from Europe and South America with respect to the species’ breeding system. We used 28S rRNA nuclear and COI mitochondrial sequence data to construct a molecular phylogeny. Phylogenetic generalized linear models were applied to examine the potential influence of morphological and life-history characters.

Results

The best-fit model revealed that the breeding system and age at sexual maturity influence sperm length in gastropods. In general, species with predominant cross-fertilization had longer sperm than species with predominant self-fertilization or a mixed breeding system. Across species with shells (snails), sperm length also increased with shell size.

Conclusions

Our study provides evidence that sperm length in stylommatophoran gastropods is influenced by the risk of sperm competition, as well as by age at sexual maturity and shell size. This finding extends present knowledge of sperm evolution to a group of so far poorly studied simultaneous hermaphrodites.


Types of Nerite Snails

There are many species of Nerite Snails. Thus, there is a great amount of variability between their color patterning and shell shapes. However, one thing stays the same about all of them, they all look gorgeous and they are awesome algae eaters.

Now, I am not going to list all types of Nerite snails, there are simply too many of them ( way too many! ). However, the most popular ones in this hobby:

  1. Zebra nerite snails (Neritina natalensis Zebra)
  2. Tiger nerite snails (Neritina turrita)
  3. Olive nerite snails (Neritina reclivata)
  4. Horned nerite snails (Neritina Clithon corona)
  5. Black (Red, Gold) Racer nerite snails (Neritina pulligera, Vittina waigiensis)
  6. Red Spotted nerite snails (Neritina natalensis sp)

Have you noticed that in articles authors usually use common and scientific name when they talk about shrimp or fish? What about Nerite snails?

In most cases, you will not see their scientific names in the articles and guides. Do you know why? Because everything is just too confusing and nobody knows for sure who is who. For example, let’s take a Tiger nerite snail. We have Neritina turrita (Chemnitz, 1786) and Neritina turrita (Gmelin, 1791). Are they the same Species?

According to one of the studies , “Nerites identification is still in the very complicated problem to solve. Some of the problems such as shell polymorphism, synonyms or multiple names that are used by the author, then it has not been published and identified”.

It took me some time to find the scientific name of Black Racer nerite snail and, actually, I am not 100% sure that it is right. Maybe it also belongs to Vittina waigiensis species. Nonetheless, despite all this mess, adult Nerite snails (on average) share approximately the same parameters and water requirements.


Bean-Counter Evolution

In this simulation game, teams of predators equipped with genetically different “mouths” (utensils) hunt for “prey” (assorted beans). Over several “generations” of play, the fittest among the predators and prey dominate the population, modeling the evolutionary process of natural selection.

Note: This game works best with a group of 15 or more people. See Teaching Tips, below, for ways to accommodate smaller groups.

Tools and Materials

  • Dry beans of four different colors, such as kidney or red beans, navy beans (white), black beans, and pinto beans a few hundred of each type (a one-pound bag of each should be enough)
  • Four plastic containers (one for each color of bean)
  • Bowl or box for mixing the beans
  • Plastic or paper cups (one per person)
  • Predator "mouths” of several types, such as plastic forks, knives, spoons, chopsticks, forceps, straws, or bare hands (one per person in each predator group, plus extras for “predators” that change groups during the game see details below)
  • Stopwatch, or a watch with a second hand
  • Level, outdoor area of grass, sand, or bare dirt, roughly a 15 x 15 feet (5 x 5 meters) square indoor, carpeted areas can be substituted
  • Three or more large sheets of butcher paper, flip chart, or other means of recording and displaying results
  • Markers of several colors (for recording results)
  • Calculators (one per predator group)

Assembly

  1. Mark off a zone about 15 x 15 feet (5 x 5 meters) square to serve as a habitat. Be careful not to use any materials that could potentially trip or injure someone. You can also designate existing landmarks, such as trees or sidewalks, to mark the boundaries of the habitat.
  2. Count out 100 of each of the four different-colored beans and place them into a container. Mix thoroughly.
  3. Using a marker, make grids on your butcher paper or flip chart so you can keep track of at least three generations of data. The data grid of a sample game is shown below.
  4. Divide participants into three or more equal-sized predator groups (five or six people per group is optimal, but other sizes will work). You’ll also need one person to keep time (the Timer), and one or more individuals to set up and adjust the bean numbers over the generations, record the data, and enforce the rules.
  5. Randomly assign each predator group a type of “mouth.” For instance, one group might use their dominant hand (one hand only) others might use forks, knives, spoons, or chopsticks.
  6. Give each predator a cup. It will serve as their “stomach.”
  7. Review these rules with participants:
    a. All bean-prey are of equal value.
    b. Only the assigned “mouth” can be used to capture prey.
    c. Captured prey must be placed into the stomach-cup to count.
    d. Prey may not be scraped or shoved into the stomach-cup the cup must never touch the ground.
    e. Prey may be captured from another predator’s mouth, but not from another predator’s stomach.
    f. All predators must stay outside the habitat until the hunt begins (when the Timer calls “GO!”)
    g. Each round of hunting lasts one minute.
    h. All predators must stop hunting as soon as time is called (when the Timer calls “STOP!”) prey that is in the mouth, but not yet in the stomach, must be dropped.

To Do and Notice

Each round of this game has three steps:

Step 1: Predators hunt their prey, and data from the hunt is collected
Step 2: Predator groups are adjusted for size, representing the relative success of each predator type
Step 3: Prey groups are adjusted for size, representing the relative survival rate of each prey type

Each one-minute round of play represents one reproductive generation for both predators and prey. After the first round, calculations are done, adjustments made, and subsequent rounds are played. Ideally, participants should play at least three rounds before examining the final results.

Let the Hunt Begin!
Begin with predators gathered, standing with their backs to the habitat. The designated Timer then spreads the initial 400 prey beans randomly around the habitat, and then calls "GO!"

Predators turn around, enter the territory, and collect as many prey as possible—while following the rules. After one minute, the Timer calls "STOP!" All predators stop hunting and participants gather with their group outside the habitat. If any predator is caught violating the rules, they and the beans they have captured are eliminated from the group.

Collect Data and Adjust Group Sizes for Each Additional Generation
Step 1: Gather data for each group: Have members tally the number of captures for each type of bean, and add them together. For example, if the five members of the Hand Group captured 10, 8, 4, 7, and 3 red prey, respectively, their group captured 32 red prey in total.

Record data for each group in the Generation 1 table, filling in the rest of the chart as indicated. When all data are recorded, add together the total number of prey captured by all groups and divide by the number of groups to calculate the average number of prey captured.

Step 2: Adjust for the number of predators surviving:Before playing the next round (Generation 2), use the average number of prey captured to adjust group sizes—a change that represents the relative success of each kind of predator.

Groups that captured more than the average number of prey gain a member those that captured fewer than the average number of prey lose a member. For example, if the Chopsticks Group captures fewer than the average number of prey, and the Hand Group captures more than the average number of prey, one member of the Chopsticks Group is transformed into a member of the Hand Group for the next round.

Step 3: Adjust for the number of prey surviving: Likewise, use the data generated to adjust the size of the prey groups to represent the survival rate of each type.

Find the number of each prey type remaining in the habitat at the end of the round. Since each type of prey (color of bean) started with 100 individuals, the number remaining for the first round will be the original 100, minus the total number of prey type captured. For example, if all predators together captured a total of 11 black-bean prey, there would be 89 remaining.

Assume that each remaining prey member will reproduce one individual. So—for this example—we would count out an additional 89 black beans and put them in the bowl. Repeat this process for each of the remaining prey types.

Play Subsequent Generation Rounds and Evaluate Results
Complete as many rounds as time allows—ideally, three generations or more. Be sure to adjust the predator and prey numbers after each generation, and spread the additional prey beans randomly around the habitat before the start of each new round of “hunting.”

When you’re done, examine the results. Do you see any trends in population numbers? What explanation(s) might account for these trends? Did any of the types of predator or prey go “extinct”? Why?

What’s Going On?

In this simulation, you can witness a biological process known as natural selection play out in real time before your eyes.

All living creatures—yourself included—have traits determined in part by genetics. These traits, inherited from your parents, are called heritable traits. Your own survival, and the survival of your species, depends on how well these traits equip you for success in your environment. This idea is captured in the phrase “survival of the fittest.”

To be clear, evolutionary fitness has nothing to do with working out at the gym. Instead, it refers to the traits, determined by genes, which equip a population to survive and reproduce in a particular habitat.

Traits that enhance the survival and reproductive fitness of an individual are passed along to future generations in that population. Traits that are detrimental, or do not allow an organism to adequately compete for resources, tend to cause that organism to die early, leaving few or no progeny. Over millions of years, natural selection has resulted in the astonishing variety of organisms that inhabit the earth.

As you play this game over several generations, you’ll see that some predator variants are more evolutionarily fit—that is, better equipped—to capture prey (resources) than others. As a result, more offspring survive and pass along this trait. The variants that catch the fewest number of prey are not evolutionarily fit. They do not reproduce well, so their numbers are reduced with each round.

Likewise, certain populations of bean-prey evade capture more successfully than others. In this simulation, we assume each prey survivor reproduces one individual in each generation. Those variants that elude predation go on to reproduce, and their numbers increase. Those that are more easily preyed upon do not reproduce their numbers decrease, and they may eventually become extinct.

Going Further

Tell participants that one of the predator groups has very low genetic variability because they've been isolated for so long. A disease ravages the entire population, modifying or destroying their prey-capturing tools. Simulate the change by altering the predator’s ability to hunt—breaking the tines on forks, for instance, or allowing the Hand Group to use only one finger. These groups will rapidly decrease in size over a few generations. This change illustrates the danger that lack of diversity in a population presents.

Teaching Tips

This activity can be simplified by having only one type of prey, or one type of predator.

Being a predator includes bending down and occasional physical contact, so some participants may not be able or willing to participate. Those who do not become “predators” can fill one of many non-predator roles, such as starting and stopping the timer, helping to gather and post data, counting out the beans for the next generation, or serving as a referee to enforce the rules.

Data may be graphed to facilitate visualizing changes in predator and prey populations over time. For example, a line graph could show the number of generations on the x-axis, and the number of each different bean type on the y-axis, using different colors of ink or symbols to track each bean type. A similar graph could track the change in predator numbers over the generations.

A single activity cannot address the complexities of all evolution, natural selection, and predator/prey interactions. You may want to lead a discussion about other factors involved in evolution, such as migration, mutation, and natural disasters.


DISCUSSION

Life history response to size selection

The growth pattern of Helix aspersa snails resembled a biphasic logistic-like trajectory, with a phase of accelerating growth early in ontogeny and a phase with decelerating growth later in life(Fig. 1). Selection for increased adult size substantially changed the characteristics of this growth:the size-selected snails attained larger initial size M0and higher maximum growth rate GRmax, and their growth curve asymptotic size MA was almost double that of the control snails (Table 1). Development of larger adult size can proceed through three mechanisms, which are not mutually exclusive: by starting growth from larger initial size, by speeding-up size-specific growth, and by extending the growth period. Our data indicate that size-selection of H. aspersa snails produced larger adults via an increase of egg size and of the size-specific growth rate (Tables 1, 2, Fig. 2B). The evolution of adult size was not achieved through alteration of developmental rates because the two lines attained the maximum growth rate at similar ages and entered the adult stage at comparable rates. To further probe the relative role of initial size and growth rate in size evolution, egg size would need to be manipulated in order to break the potential covariance between the early physiological state determined by egg size and growth performance later in life(Sinervo and Huey, 1990).

Comparison of size-scaling of oxygen consumption (A–C) and shell mass(D–F) of control and size-selected Helix aspersa snails in the fast- and slow-growth phases of ontogeny. Growth rate accelerates with age in the fast-growth phase it decelerates with age in the slow-growth phase. Symbols denote measures of individual snails.

Comparison of size-scaling of oxygen consumption (A–C) and shell mass(D–F) of control and size-selected Helix aspersa snails in the fast- and slow-growth phases of ontogeny. Growth rate accelerates with age in the fast-growth phase it decelerates with age in the slow-growth phase. Symbols denote measures of individual snails.

Increased growth rates are achieved through either (1) an increase of energy acquisition, (2) an increase of resource allocation to growth at the expense of other energy-demanding processes (e.g. reproduction, maintenance),or (3) lowering of the metabolic costs of growth(Glazier, 1990 Konarzewski, 1995 Czarnołęski and Kozłowski, 1998 Bayne,1999 Konarzewski et al.,2000). In general, accelerated growth is expected to increase total metabolism as a result of elevated expenditures for biosynthesis and tissue deposition (Jörgensen,1988), but the interdependence of mechanisms 1–3 can lead to different responses of total metabolism(Konarzewski, 1995). For example, fast-growing forms of the lake whitefish Coregonus clupeaformis had lower food consumption and lower metabolism than slow-growing dwarfs (Trudel et al.,2001) artificial selection for increased body size in oysters produced fast-growing individuals which consumed more food but used less oxygen due to lower costs of growth (joules respired per joule of growth) and decreased expenditure for maintenance(Bayne, 1999). Interestingly,MacLaury and Johnson (MacLaury and Johnson, 1972) demonstrated that selection for increased oxygen uptake can produce slow-growing organisms. In our study, fast- and slow-growing lines of H. aspersa had similar food consumption. Compared to the control line, the fast-growing selected line had higher growth efficiency (Table 2, Fig. 2C), and a lower (at smaller body sizes) or equal (at larger sizes) metabolic rate(Fig. 3C). These characteristics point to the role of alteration of resource allocation (2) and costliness of growth (3) in differentiating growth rates between the two lines. Evolution of growth rates through resource allocation must involve alterations in the energy provisioning of many functions which are interconnected in complex ways, thus generating a wide array of different tradeoffs (Metcalfe and Monaghan,2001 Pigliucci and Preston,2004 Czarnołęski et al., 2005). This study was not aimed at identifying such tradeoffs, but our data allow us to look at whether size-selected snails enhanced their growth at the expense of survivorship and shell production. We found a concerted response of shell production and oxygen consumption to size selection: in the phase of accelerating growth, the fast-growing selected line had a lower metabolic rate and produced lighter shells than the slow-growing control (Fig. 3C,F). Interestingly, the difference in metabolic rate persisted as long as the size-selected snails had lower shell mass than control snails: both lines became similar with respect to metabolic rates after attainment of body size MF equal to 0.498 g, which almost exactly coincided with equalization of shell masses in the two lines at MF=0.490 g. Our results suggest that the increased expenditure for tissue growth in the size-selected snails was at least in part covered at the expense of shell production. Costs of shell production are often considered an important part of the energy budget, and they are responsible for tradeoffs between shell elongation and thickening (Palmer,1992) (but see Czarnołęski et al.,2006). Our analysis of snail mortality suggests that increased growth rate was not realized at the expense of processes that determined survivorship (e.g. maintenance). On the contrary, the mortality rate tended to be lower in the fast-growing selected line than in the slow-growing control line. We admit, however, that this finding might not be conclusive because,for logistical reasons, we only measured juvenile mortality, in laboratory conditions, under high food levels and in the absence of natural enemies. Adverse effects of increased growth early in life are often not evident until much later (Metcalfe and Monaghan,2001 Monaghan and Haussmann,2006) a fuller understanding of the costs of growth in snails would require analyses of lifespan and mortality under unfavorable conditions(infections, starvation, dehydration, hypothermia, estivation). For example,the impairment of shell production in the selected snails suggests their higher susceptibility to water loss through the shell, and less ability to withstand predatory attacks.

Growth rate and metabolic scaling

Expenditure for growth processes can constitute a significant part of total metabolism: in the toad Bufo bufo it reaches 60% of total metabolism(Jörgensen, 1988). Given that in fast-growing organisms the expenditure for biosynthesis and tissue deposition increases, and that the growth rate changes proportionally to body size, total metabolism is predicted to scale isometrically or almost isometrically with body mass in fast growers, and negatively allometrically in slow growers (Wieser, 1994 Riisgård, 1998). Reviving Bertalanffy's idea (von Bertalanffy, 1957), Glazier(Glazier, 2005) used this concept to distinguish four major types of intraspecific metabolic scaling,and he argued that much of the variability of metabolic scaling between organisms (individuals, species and higher taxa) can be explained by the effects of evolution of differential growth rates. For example, according to Glazier (Glazier, 2006),isometric metabolic scaling prevails in pelagic species because they evolved fast growth, whereas negative allometry dominates in benthic species growing relatively slowly. The results of our analysis of metabolic scaling in H. aspersa snails are generally consistent with the concept of coupling between growth rates and metabolic scaling. The size-dependence of metabolism was isometric or almost isometric in the fast-growing, early ontogenetic stages of snails (b=1.03 in the size-selected line, b=0.92 in the control line), and it was negatively allometric in the slow-growing late stages(b=0.74 in the size-selected line, b=0.75 in the control line)(Table 4, Fig. 3A,B) the ontogenetic shallowing of metabolic scaling was statistically significant in the selected but not in the control line (Table 3). The biphasic metabolic scaling detected in H. aspersaresembles Glazier's Type III, and it has been reported in a wide range of different organisms including copepods, marine invertebrates, insects, fish and mammals (Brody, 1945 Epp and Lewis, 1980 Muthukrishan and Pandian,1987 Post and Lee,1996). For example, the metabolism of fast-growing Mytilus edulis larvae and juveniles increased almost isometrically with size(b=∼0.9) and negatively allometrically (b=∼0.7) in slow-growing adult mussels (Riisgård,1998). Our data also point to the importance of the growth rate in explaining the between-organism variability of the mass exponent for metabolism: scaling of metabolism was steeper in the fast-growing selected line than in the slow-growing control(Table 3, Fig. 3C note that this difference persists only early in ontogeny).

Size-scaling of metabolism can be obscured by the allometry of metabolically inert biomass such as reserve and skeletal material(Glazier, 1991). For example,in the amphipod Gammarus fossarum, whose proportion of metabolically active protoplasm decreases while the proportion of metabolically inert chitin increases with body size, metabolism scaled to the power of 0.65 with whole body mass, but to the power of 0.95 in relation to protoplasm(Simčič and Brancelj,2003). This demonstrates that an examination of coupling between metabolic scaling and growth rates in molluscs should incorporate changes in shell mass. Our data showed that the shell mass of H. aspersa snails constituted up to 68% of whole body mass its size-scaling differed between the early and late phases of snail development(Table 3, Fig. 3D,E). Shell mass scaled to the power of 0.79 (selected line) and 0.72 (control line) with flesh mass in the fast-growth phase, and to the power of 0.98 and 1.02 in the slow-growth phase (Table 4), which means that the proportion of metabolically inert shell decreased with body size during early growth and remained approximately constant throughout the remainder of life. Although this suggests that shell size-scaling may have affected our assessment of scaling of metabolism in the early (but not in the late) ontogenetic stages, the exponents for H. aspersa metabolism derived from the regressions of metabolism versus shell-free mass resembled the estimates calculated from the regressions of metabolism versus whole mass (Table 4). This result is similar to earlier findings(Simčič and Brancelj,2003) that the metabolism of the amphipod G. fossarumscaled at similar rates with whole and with non-chitinous mass, despite the increase in the proportion of metabolically inert exoskeleton with body size. Our comparison of the size-scaling of shell in selected versuscontrol lines of H. aspersa (Tables 3, 4, Fig. 3F) revealed that scaling in the two lines was similar when analyzed in late ontogenetic stages, but early in ontogeny the proportion of shell mass increased faster with body size in the selected than in the control line. Note that this difference cannot account for our finding that the metabolism of selected snails scaled faster with whole body mass than in the control. Just the opposite: such a difference should sharpen the between-line difference in metabolic scaling when data on shell-free mass are considered instead of data on whole mass, and we found such a tendency (Table 3). Overall, removing the effects of metabolically inert shell mass did not change the general picture of size-scaling of metabolism derived from the analysis based on the whole mass of snails (Table 3). This strengthens the primary evidence on the role of growth rates in explaining variability of metabolic scaling in H. aspersasnails.


Animal Diversity Web

Achatinella mustelina is an arboreal pulmonate gastropod that is endemic to the island of O’ahu in the Hawaiian archipelago. This endangered terrestrial snail has a fairly large distribution from the southern edge of the island to the northern boundary of the Wai’anae Mountains. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992 Holland and Hadfield, 2002 Kobayashi and Hadfield, 1996)

Habitat

Achatinella mustelina inhabits elevated forests that are dry, wet, or mesic. Generally, A. mustelina attaches itself to leaves at the tops of native trees and shrubs such as Metrosideros polymorpha, Dubautia plantanginea, Myrsine lessertiana, Pisonia sandwicensis, Antidesma platyphyllum and Nestegis sandwicensis. Individuals may live on a single tree for their entire lifetime. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992 Hadfield, et al., 1993 Holland and Hadfield, 2002 Killian, 2007)

  • Habitat Regions
  • tropical
  • terrestrial
  • Terrestrial Biomes
  • forest
  • mountains
  • Range elevation 600 to 1158 m 1968.50 to 3799.21 ft

Physical Description

Achatinella mustelina from different locations vary in size, shape, and color, but no specific patterns in these differences have been described. In general, adults range 19 – 24 mm in length, with an average length of 21.4 mm. The shells have a shiny finish and are usually brown with light bands that circle the suture convex, or they are white with transverse black or brown lines. Shells of A. mustelina can be either dextral or sinistral and consist of five to seven convex whirls. The shell is relatively high-spiraled and oblong to ovate with an aperture that is also oblong and ovate. The columella of A. mustelina is short, stout, and slightly twisted, and it has a well-developed spiral lamella, or ridge. A callus on the columella closes the umbilicus. The lip of the organism does not have any ridges, ribs, or folds. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992 Aubry, et al., 2005 Baily, 1943 Hadfield, et al., 1993 Killian, 2007 Schilthuizen and Davison, 2005 Welch, 1938)

  • Other Physical Features
  • ectothermic
  • heterothermic
  • bilateral symmetry
  • Range length 18.5 to 23.1 mm 0.73 to 0.91 in
  • Average length 21.4 mm 0.84 in

Development

Achatinella mustelina develops from an intrauterine embryo, and its growth in utero is thought to be logarithmic. Young are born live and are approximately 4.5 mm in length. The snail grows at a relatively slow rate of 2 mm per year, and over the course of four to five years, it will only grow to be five times its birth length. Growth in A. mustelina is determinate and individuals reach their maximum size before becoming reproductively mature. A unique characteristic of development in A. mustelina is that individuals of different sizes grow at the same rate. (Hadfield and Mountain, 1980 Hadfield, et al., 1993)

Reproduction

Achatinella mustelina has a lengthy gestation period and gives birth to large, live young that mature late and have a low fecundity. Although reproductive maturity occurs after the maximum size is reached, reproductive maturity may be dependent on age, not size. Reported age at maturity varies, ranging from 3 to 6.9 years. Similarly, reports of fecundity vary, but rates as low as 0.4 offspring/adult/year have been observed, as well as rates as high as 7 offspring/adult/year.

Little information about reproductive behavior in Achatinella mustelina is known, but this species is hermaphroditic and thought to breed year-round. Some species of the genus Partulina , sister to Achatinellidae, are thought to self-fertilize, so A. mustelina may self-fertilize as well. Partulina redfieldii can reproduce even in long-term absence of mates. The mechanism of this form of reproduction is not clear, however. Possibilities include parthenogenesis and long-term sperm storage, in addition to self-fertilization.

Genetic evidence suggests interchiral mating takes place for A. mustelina . Other terrestrial gastropods with high-spired shells like A. mustelina align themselves parallel and mount the other snail’s shell when mating. One snail inserts its penis in to the other and releases spermatophores. Embryos are intrauterine, and no more than two large embryos are contained in the uterus usually there is only one. The large size of newborn A. mustelina , approximately 4.5 mm in length, limits the size of the maternal snail. (Hadfield and Mountain, 1980 Hadfield, 1986 Hadfield, et al., 1993 Holland and Hadfield, 2007 Killian, 2007 Kobayashi and Hadfield, 1996 Schilthuizen and Davison, 2005)

  • Key Reproductive Features
  • year-round breeding
  • simultaneous hermaphrodite
  • sexual
  • fertilization
    • internal
    • Breeding season Achatinella mustelina breeds year-round.
    • Range number of offspring <1 per year to 7 per year
    • Range age at sexual or reproductive maturity (female) 3 to 6.9 years

    Although the literature does not include specific information about parental investment in Achatinella mustelina , in general, terrestrial gastropods do not provide parental care after birth. The most common form of parental investment for terrestrial gastropods comes in the form of calcium carbonate and other nutrients given to the developing egg. (Baur, 1994)

    Lifespan/Longevity

    Achatinella mustelina has a relatively long lifespan compared to other terrestrial gastropods. Longevity is estimated to be 10 years, but individuals may live up to 15 or 20 years. (Hadfield, et al., 1993 Killian, 2007)

    Behavior

    The Oahu tree snail is a terrestrial snail that is primarily found in native Hawaiian trees, such as Osmanthus sandwicensis, Gouldia sp., Metrosideros polymorpha, and large bushes. Generally, this snail attaches to leaves at the tops of native trees and shrubs, and is nocturnal. Individuals of A. mustelina enter a stage of inactivity during the numerous dry periods of its environment, curtailing feeding and growth. Individuals are not highly motile, resulting in many small, relatively isolated populations of A. mustelina . (Hadfield, et al., 1993 Holland and Hadfield, 2007 Killian, 2007)

    Home Range

    The home range of A. mustelina is often limited to a single tree and the nearby surrounding shrubbery. Individuals rarely move between trees.

    Communication and Perception

    Achatinella mustelina , like most terrestrial gastropods, communicates through both touch and chemical signaling, using the lower set of head tentacles. Individuals transmit pheromone signals both through direct contact and through the mucous trail left during locomotion. This includes warning of predator presence.

    Achatinella mustelina has simple eyes for visual perception, albeit limited to larger objects. However, vision is not a primarily means of searching or foraging, given the snail’s nocturnal habits. (Chelazzi, 1990 Pakarinen, 1991)

    • Communication Channels
    • tactile
    • chemical
    • Other Communication Modes
    • pheromones
    • Perception Channels
    • visual
    • tactile
    • chemical

    Food Habits

    Achatinella mustelina feeds primarily at night. This species is a mycophage, grazing upon epiphytic fungi growing on the bark or leaves of native plant species, such as Osmanthus sandwicensis, Gouldia sp. or Metrosideros polymorpha. Few imported species of plant are suitable for the fungi eaten by this snail species. In captivity, A. mustelina has been grown on cornstarch or sooty mold, with a supplement of cuttlebone providing the calcium necessary for shell growth. (Killian, 2007 Kobayashi and Hadfield, 1996)

    Predation

    The primary predator of Achatinella mustelina is the introduced carnivorous snail, Euglandina rosea, and A. mustelina has no defense mechanisms for this species. Several rat species eat A. mustelina , particularly the larger individual snails. Other foreign species that prey upon A. mustelina include the terrestrial flatworms Geoplana septemlineata and Platydemis manokwari . The Hawaiian Thrush ( Phaerornis obscura ) eats A. mustelina , although it isn't the bird's primary food source. (Hadfield, et al., 1993 Hart, 1978 Killian, 2007)

    • Known Predators
      • Rats, Murinae
      • Rosy wolfsnail, Euglandina rosea
      • terrestrial flatworm, Geoplana septemlineata
      • New Guinea flatworm, Platydemis manokwari
      • Hawaiin thrush, Phaerornis obscura

      Ecosystem Roles

      Achatinella mustelina consumes fungi from plant bark and leaves. Historically, A. mustelina had no natural predators that relied upon it as a food source. With the introduction of the predatory snail Euglandina rosea, A. mustelina , along with other sympatric members of the genus Achetinella have become prey for this species. (Hadfield and Mountain, 1980)

      Economic Importance for Humans: Positive

      Due to their vibrant coloration, Achatinella mustelina shells were collected by human inhabitants of the island of Oahu to craft traditional leis and other ornaments. Shells from the genus Achatinella are still collected and sold as ornaments today as part of Hawaii’s tourist trade. (Hart, 1978)

      Economic Importance for Humans: Negative

      There are no known negative effects of Achatinella mustelina on humans.

      Conservation Status

      Achatinella mustelina is the currently the most abundant species of the O’ahu tree snails and has been studied considerably for conservation efforts. The slow growth, long pre-reproductive life, and low fertility of A. mustelina , in conjunction with its relatively sedentary lifestyle and small geographic range, make A. mustelina populations very vulnerable to disturbances, either from predation, human collection, or habitat destruction. Lowland habitat destruction by human inhabitants for the purposes of farming and logging have reduced the geographic range of A. mustelina to only high elevation mountainous forests.

      However, the introduction of the invasive predatory snail Euglandina rosea from North America led to the rapid and widespread decline and destruction of A. mustelina populations. Euglandina rosea predates opportunistically on a number of species of terrestrial snails. Only a few hundred individuals of A. mustelina are estimated to remain in the wild. (Hadfield, 1986 Hadfield, et al., 1993)

      Contributors

      Peter Bicescu (author), The College of New Jersey, Colleen Stalter (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Renee Mulcrone (editor), Special Projects.

      Glossary

      Referring to an animal that lives in trees tree-climbing.

      having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

      uses smells or other chemicals to communicate

      animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

      union of egg and spermatozoan

      forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

      having a body temperature that fluctuates with that of the immediate environment having no mechanism or a poorly developed mechanism for regulating internal body temperature.

      fertilization takes place within the female's body

      animals that live only on an island or set of islands.

      having the capacity to move from one place to another.

      This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

      an animal that mainly eats fungus

      the area in which the animal is naturally found, the region in which it is endemic.

      islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

      reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

      chemicals released into air or water that are detected by and responded to by other animals of the same species

      the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

      reproduction that includes combining the genetic contribution of two individuals, a male and a female

      mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

      uses touch to communicate

      the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

      uses sight to communicate

      breeding takes place throughout the year

      References

      Makua Military Reservation. Final Implementation Plan for Makua Military Reservation, Island of Oahu. Schofield Barracks, HI: United States Army Garrison, Hawaii Directorate of Public Works Environmental Division. 2003. Accessed January 03, 2013 at http://manoa.hawaii.edu/hpicesu/DPW/2003_MIP/Sec_1/2003_MIP_edited.pdf.

      U.S. Fish and Wildlife Service. Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella. Portland, OR: U.S. Fish and Wildlife Service. 1992. Accessed January 06, 2013 at http://ecos.fws.gov/docs/recovery_plan/920630.pdf.

      Aubry, S., F. Magnin, V. Bonnet, R. Preece. 2005. Multi-scale altitudinal patterns in species richness of land snail communities in south-eastern France. Journal of Biogeography , 32: 985-998.

      Baily, J. 1943. Zoogeography of tree snails. Ecology , 90: 75-85.

      Baur, B. 1994. Parental care in terrestrial gastropods. Cellular and Molecular Life Sciences , 50: 5-14.

      Chelazzi, G. 1990. Eco-ethological aspects of homing behavior in mollusks. Ethology Ecology & Evolution , 2(1): 11-26.

      Hadfield, M. 1986. Extinction in Hawaiian achatinelline snails. Malacologia , 27: 67-81.

      Hadfield, M., S. Miller, A. Carwile. 1993. The decimation of endemic Hawai'ian tree snails by alien predators. Integrative and Comparative Biology , 33(6): 610-622. Accessed January 06, 2013 at http://icb.oxfordjournals.org/content/33/6/610.short.

      Hadfield, M., B. Mountain. 1980. A field study of a vanishing species, Achatinella mustelina (Gastropoda, Pulmonata), in the Waianae Mountains of Oahu. Pacific Science , 34(4): 345-358. Accessed January 06, 2013 at http://scholarspace.manoa.hawaii.edu/handle/10125/1633.

      Hart, A. 1978. The onslaught against Hawaii’s tree snails. Natural History , 87(10): 46.

      Holland, B., M. Hadfield. 2002. Islands within an island: phylogeography and conservation genetics of the endangered Hawaiian tree snail Achatinella mustelina. Molecular Ecology , 11: 365-375.

      Holland, B., M. Hadfield. 2007. Molecular systematics of the endangered O’ahu tree snail Achatinella mustelina: synonymization of subspecies and estimation of gene flow between chiral morphs. Pacific Science , 61(1): 53-66.

      Killian, H. 2007. Status of the species – Achatinella mustelina tree snails (Oahu Tree Snails). Mauka FEIS , 2(H-1): 295-450.

      Kobayashi, S., M. Hadfield. 1996. An experimental study of growth and reproduction in the Hawaiian tree snails Achatinella mustelina and Partulina redfieldii (Achatinellinae). Pacific Science , 50: 338-354.

      Pakarinen, E. 1991. Feeding avoidance of terrestrial gastropods to conspecific and nonspecific material. Journal of Molluscan Studies , 58(2): 109-120.

      Schilthuizen, M., A. Davison. 2005. The convoluted evolution of snail chirality. Naturwissenschaften , 92: 504-515.


      Snails signal a humid Mediterranean

      An international team of researchers has shown that old wives' tales that snails can tell us about the weather should not be dismissed too hastily.

      While the story goes that if a snail climbs a plant or post, rain is coming, research led by the University of York goes one better: it shows snails can provide a wealth of information about the prevailing weather conditions thousands of years ago.

      The researchers, including scientists from the Scottish Universities Environmental Research Centre (SUERC), analysed the chemistry of snail shells dating back 9,000 to 2,500 years recovered from Mediterranean caves, looking at humidity at different times in the past.

      Their findings, which are reported in the journal Quaternary International, reveal that when the first farmers arrived in Italy and Spain, the western Mediterranean was not the hot dry place it is now, but warmer, wetter and stickier.

      The research was led by Dr André Carlo Colonese from York's Department of Archaeology.

      Dr Colonese and his co-authors believe that land snails have great potential as a source of information about human behaviour and palaeoclimatic conditions and therefore should be given much more attention.

      Dr Colonese, an EU Marie Curie Fellow in York's Centre for Human Palaeoecology & Evolutionary Origins, said: "By putting together research on snails from multiple sites across Spain and Italy, we were able to produce a large scale regional picture for weather conditions over the western Mediterranean area.

      "This allowed us to observe differences in climate across the region. Interestingly, when compared with previous studies, we found that while conditions on the Atlantic coast of northern Spain were probably much like those of today, on the Mediterranean side in locations such as southern Spain and Sicily, conditions were much more humid."

      Archaeological sites around the Mediterranean basin contain an abundance of land snail shell remains. The researchers selected well-preserved shells for isotopic analysis from the early to late Holocene layers, covering the Mesolithic, Neolithic, Chalcolithic and Bronze Age periods. They looked at the oxygen and carbon isotopic compositions of the shells of Pomatias elegans (or the round-mouthed snail as it is more commonly known), comparing those found in the Iberian Peninsula sites with modern shells of the same species.

      Co-author Dr Giovanni Zanchetta, from the Earth Science Department at the University of Pisa, Italy, said: "Stable isotopes on land snail shells have represented a challenge for researchers for years, but using archeological well-dated sites, new fundamental insight on past climate are coming along. And we are just at the beginning because there are a lot of excavations which can yield rich material."

      The shell stable isotope measurements were carried out at SUERC, East Kilbride, Scotland, using a mass spectrometer. Further analysis was performed at the Cornell Stable Isotope Laboratory in the United States.

      Co-author Professor Tony Fallick of SUERC and Professor of Isotope Geosciences at the University of Glasgow said: "This is a classic example of multidisciplinary research where colleagues from a variety of backgrounds including archaeology, climate and environmental science, and geochemistry collaborate to deliver insights into our recent past that have societal impact."


      Class Scaphopoda

      Members of class Scaphopoda (&ldquoboat feet&rdquo) are known colloquially as &ldquotusk shells&rdquo or &ldquotooth shells,&rdquo as evident when examining Dentalium, one of the few remaining scaphopod genera. Scaphopods are usually buried in sand with the anterior opening exposed to water. These animals bear a single conical shell, which has both ends open. The head is rudimentary and protrudes out of the posterior end of the shell. These animals do not possess eyes, but they have a radula, as well as a foot modified into tentacles with a bulbous end, known as captaculae. Captaculae serve to catch and manipulate prey. Ctenidia are absent in these animals.

      Figure (PageIndex<1>): The Scaphopods: The Scaphopods (&ldquoboat feet&rdquo) include the Antalis vulgaris, the shell of which is depicted here.


      Geological history

      Biological events in gastropod history. BGS ©UKRI. All rights reserved.

      The first gastropods evolved from an unknown bilaterally symmetrical mollusc ancestor in the early Cambrian, but they became common during Palaeozoic times. Between the Cambrian and Devonian, gastropods were entirely marine, but by the Carboniferous some had entered non-marine waters and land snails may have evolved by the late Carboniferous.

      At the end of Permian times there was a mass extinction event, and gastropods did not escape. However, with the Mesozoic, many new species evolved, including high spired, burrowing forms and some gastropods grew to an enormous size (e.g. some of the cowry shells). Gastropods colonised marine, brackish and freshwater habitats as well as the land by this time.

      The maximum development of the gastropods has been in the last 65 million years following the end-Cretaceous mass extinction event. This was a time of rapid evolutionary radiation of benthic (bottom-dwelling) species and, starting in the early Eocene, pelagic pteropods evolved as well. Terrestrial gastropods became particularly common during the Palaeogene and it was probably at this time that shell-less gastropods also developed, but they are not found as fossils.

      In all about 105 000 living and 15 000 fossil gastropod species are known.


      Birds and Mammals

      The rocky shore is also visited by many birds and marine mammals as a place to rest, warm up and to breed. Many seabird species, such as penguins, shags, gannets, and albatross, use the rocky shore as a nesting area and to dry off and warm up after a cold swim. If you are lucky enough to live or visit an area with seals or sea lions, chances are you will find them basking in the sun on the rocky shore, warming up after a cold swim.


      Watch the video: Επεξεργασία Σαλιγκαριών (November 2022).