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4.9: Sexual dimorphism - Biology

4.9: Sexual dimorphism - Biology


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What, biologically, defines whether an organism is female or male, and why does it matter? The question is largely irrelevant in unicellular organisms with multiple mating types. For example, the microbe Tetrahymena has seven different mating types, all of which appear morphologically identical. An individual Tetrahymena cell can mate with another individual of a different mating type but not with an individual of the same mating type as itself. Mating involves fusion and so the identity of the parents is lost; the four cells that result are of one or the other of the original mating types.

In multicellular organisms, the parents do not themselves fuse with one another. Rather they produce cells, known as gametes, which do. Also, instead of two or more mating types, there are usually only two sexes, male and female. This, of course, leads to the question, how do we define male and female? The answer is superficially simple but its implications are profound. Which sex is which is defined by the relative size of the fusing cells the organisms produce. The larger fusing cell is termed the egg and an organism that produces eggs it is termed a female. The smaller fusing cell, which is often motile (while eggs are generally immotile), is termed a sperm and organisms that produce sperm are termed a male. At this point, we should note the limits of these definitions. There are organisms that can change their sex, which is known generically as sequential hermaphroditism. For example, in a number of fish it is common for all individuals to originally develop as males; based on environmental cues, the largest of these males changes its sex to become female. Alternatively, one organism can produce both eggs and sperm; such an organism is known as a hermaphrodite.

The size difference between male and female gametes changes the reproductive stakes for the two sexes. Simply because of the larger size of the egg, the female invests more energy in its production (per egg) than a male invests in the production of a sperm cell. It is therefore relatively more important, from the perspective of reproductive success, that each egg produce a viable and fertile offspring. As the cost to the female of generating an egg increases, the more important the egg’s reproductive success becomes. Because sperm are relatively cheap to produce, the selection pressure associated with their production is significantly less than that associated with producing an egg. The end result is that there emerges a conflict of interest between females and males. This conflict of interest increases as the disparity in the relative investment per gamete or offspring increases.

This is the beginning of an evolutionary economics, cost-benefit analysis. First there is what is known as the two-fold cost of sex, which is associated with the fact that each asexual organism can produce offspring but that two sexually reproducing individuals must cooperate to produce offspring. Other, more specific factors influence an individual’s reproductive costs. For example, the cost to a large female laying a small number of small eggs that develop independently is less than that of a small female laying a large number of large eggs. Similarly, the cost to an organism that feeds and defends its young for some period of time after they are born (that is, leave the body of the female) is larger than the cost to an organism that lays eggs and leaves them to fend for themselves. Similarly, the investment of a female that raises its young on its own is different from that of the male that simply supplies sperm and leaves. As you can imagine, there are many different reproductive strategies (many more than we can consider here), and they all have distinct implications. For example, a contributing factor in social evolution is that where raising offspring is particularly biologically expensive, cooperation between the sexes or within groups of organisms in child rearing can improve reproductive success and increase the return on the investment of the organisms involved. It is important to remember (and be able to apply in specific situations) that the reproductive investments, and so evolutionary interests, of the two sexes can diverge dramatically from one another, and that such divergence has evolutionary and behavioral implications .

Consider, for example, the situation in placental mammals, in which fertilization occurs within the female and relatively few new organisms are born from any one female. The female must commit resources to supporting the new organisms from the period from fertilization to birth. In addition, female mammals both protect their young and feed them with milk, using specialized mammary glands. Depending on the species, the young are born at various stages of development, from the active and frisky (such as goats) to the relatively helpless (humans). During the period when the female feeds and protects its offspring, the female is more stressed and vulnerable than other times. Under specific conditions, cooperation with other females can occur (as often happens in pack animals) or with a specific male (typically the father) can greatly increase the rate of survival of both mother and offspring, as well as the reproductive success of the male. But consider this: how does a cooperating male know that the offspring he is helping to protect and nurture are his? Spending time protecting and gathering food for unrelated offspring is time and energy diverted from the male’s search for a new mate; it will reduce the male’ s overall reproductive success, and so is a behavior likely to be selected against. Carrying this logic out to its conclusion can lead to behaviors such as males guarding of females from interactions with other males.

As we look at the natural world, we see a wide range of sexual behaviors, from males who sexually monopolize multiple females (polygyny) to polyandry, where the female has multiple male “partners.” In some situations, no pair bond forms between male and female, whereas in others male and female pairs are stable and (largely) exclusive. In some cases these pairs last for extremely long times; in others there is what has been called serial monogamy, pairs form for a while, break up, and new pairs form (this seems relatively common among performing arts celebrities). Sometimes females will mate with multiple males, a behavior that is thought to confuse males (they cannot know which offspring are theirs) and so reduces infanticide by males133.

It is common that while caring for their young, females are reproductively inactive. Where a male monopolizes a female, the arrival of a new male who displaces the previous male can lead to behaviors such as infanticide. By killing the young, the female becomes reproductively active and able to produce offspring related to the new male. There are situations, for example in some spiders, in which the male will allow itself to be eaten during the course of sexual intercourse as a type of nuptial gift, which both blocks other males from mating with a female (who is busy eating) and increases the number of offspring that result from the mating. This is an effective reproductive strategy for the male if its odds of mating with a female are low: better (evolutionarily) to mate and die than never to have mated at all. An interesting variation on this behavior is described in a paper by Albo et al134. Male Pisaura mirablis spiders offer females nuptial gifts, in part perhaps to avoid being eaten during intercourse. Of course, where there is a strategy, there are counter strategies. In some cases, instead of an insect wrapped in silk, the males offer a worthless gift, an inedible object wrapped in silk. Females cannot initially tell that the gift is worthless but quickly terminate mating if they discover that it is. This reduces the odds of a male’s reproductive success. As deceptive male strategies become common, females are likely to display counter strategies. For example, a number of female organisms store sperm from a mating and can eject that sperm and replace it with that of another male (or multiple males) obtained from subsequent mating events135. There is even evidence that in some organisms, such as the wild fowl Gallus gallus, females can bias against fertilization by certain males, a situation known as cryptic female choice, cryptic since it is not overtly visible in terms of who the female does or does not mate with136. And so it goes, each reproductive strategy leads, over time, to counter measures137. For example, in species in which a male guards a set of females (its harem), groups of males can work together to distract the guarding male, allowing members of their group to mate with the females. These are only a few of the mating and reproductive strategies that exist in the living world138. Molecular studies that can distinguish an offspring’s parents suggest that cheating by both males and females is not unknown even among highly monogamous species. The extent of cheating will, of course, depend on the stakes. The more negative the effects on reproductive success, the more evolutionary processes will select against it.

In humans, a female can have at most one pregnancy a year, while a totally irresponsible male could, in theory at least, make a rather large number of females pregnant during a similar time period. Moreover, the biological cost of generating offspring is substantially greater for the female, compared to the male139. There is a low but real danger of the death of the mother during pregnancy, whereas males are not so vulnerable, at least in this context. So, if the female is going to have offspring, it would be in her evolutionary interest that those offspring be as robust as possible, meaning that they are likely to survive and reproduce. How can the female influence that outcome? One approach is to control fertility, that is, the probability that a “reproductive encounter” results in pregnancy. This is accomplished physiologically, so that the odds of pregnancy increase when the female has enough resources to successfully carry the pregnancy to term. It should be noted that these are not conscious decisions on the part of the female but physiological responses to various cues. There are a number of examples within the biological world where females can control whether a particular mating is successful, i.e., produces offspring. For example, female wild fowl are able to bias the success of a mating event in favor of dominant males by actively ejecting the sperm of subdominant males following mating with a more dominant male, a mating event likely to result in more robust offspring, that is, off-spring more likely to survive and reproduce140. One might argue that the development of various forms of contraception are yet another facet of this type of behavior, but one in which females (and males) consciously control reproductive outcomes.


4.9: Sexual dimorphism - Biology

Male (♂) is the sex of an organism that produces the gamete known as sperm, which fuses with the larger female gamete, [1] [2] [3] or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. [4] Most male mammals, including male humans, have a Y chromosome, [5] [6] which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically however, species such as Cymothoa exigua change sex depending on the number of females present in the vicinity. [7]

Male can also be used to refer to gender.

Overview

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). [8] [9] The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. [10]

Accordingly, sex is defined across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another. [9] [11] [12]

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants. [ citation needed ]

Symbol and usage

Symbol

A common symbol used to represent the male sex is the Mars symbol ♂, a circle with an arrow pointing northeast. The Unicode code-point is:

U+2642 ♂ MALE SIGN (HTML &#9794 · &male )

The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is sometimes seen as a stylized representation of the shield and spear of the Roman god. Mars. According to Stearn, however, this derivation is "fanciful" and all the historical evidence favours "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 1588–1683)" that it is derived from θρ, the contraction of a Greek name for the planet Mars, which is Thouros. [13]

Usage

In addition to its meaning in the context of biology, male can also refer to gender [14] or a shape of connectors. [15] [16]

Sex determination

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species have only two sexes (either male or female), [8] [9] [17] hermaphroditic animals, such as worms, have both male and female reproductive organs. [18]

Genetic determination

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including humans, to be XX male or have other karyotypes. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. [19]

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. [20] The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development [21] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development. [22]

The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid. [ citation needed ]

Environmental determination

In some species of reptiles, such as alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. [23] In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. [24]

In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia. [ citation needed ]

Secondary sex characteristics

In those species with two sexes, males may differ from females in ways other than the production of spermatozoa.

In many insects and fish, the male is smaller than the female.

In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism.

In mammals, including humans, males are typically larger than females. [25]

In humans, males have more body hair and muscle mass. [26]

In birds, the male often exhibits a colorful plumage that attracts females. [27]


Species recognition and sexual dimorphism in Proconsul and Rangwapithecus *

The taxonomy of the early Miocene hominoid genera Proconsul and Rangwapithecus is re-examined. The recognition of sexual dimorphism and the identification of sex dimorphs among canine specimens is made an important element in the sorting of specimens into phena and the allocation of these to species hypodigms. I propose that specimens from Rusinga and Mfwangano previously identified as Proconsul africanus, including the well known 1948 skull, are actually females of P. nyanzae. P. africanus specimens from Songhor and the type site of Koru differ from Rusinga and Mfwangano specimens formerly placed in P. africanus. Accordingly, P. africanus sensu stricto is restricted to Koru and Songhor and Proconsul nyanzae is restricted to Rusinga and Mfwangano. Previous characterizations of P. africanus were based almost entirely upon specimens from Rusinga, and should therefore now be applied to female P. nyanzae instead the paleobiology of P. africanus and P. nyanzae must now be reconsidered. As a result of the reassignment of the Rusinga Proconsul specimens, P. nyanzae exhibits degrees of postcanine metric variability exceeding those of living catarrhines. It is suggested that this reflects in part a true species characteristic, perhaps related to an exceptional amount of size dimorphism, and in part a preservational artifact relating to the time-accumulated nature of the fossil sample. These results have implications for the systematics of other Miocene hominoid species.


Materials and Methods

Study area and data collection

The study site, Alax Zuoqi (38.85°N, 105.63°E 1448 m above sea level), Inner Mongolia, China is located at the northeastern margin of the Tengger Desert. The predominant land form is semi-desert grassland with a vegetation cover (mainly grass) of less than 15% [16]. The climate is semi-arid with a mean annual precipitation of 207.5±9.6 mm (n = 30 years) and mean annual temperature of 8.7±0.1°C (n = 30 years). A single mark-recapture quadrat of 50 m×50 m with a 20 m buffer zone was established in April 2008.

The quadrat was visited monthly between April and October (during the first third of the month), from 2008 to 2010. Lizards were collected by hand and numbered with a unique toe-clip, and their sex was determined by the presence or absence of hemipenes. Because it was difficult to distinguish male and female lizards until the hemipenes were well developed, the sex of juveniles was not determined until they were 3 months old. The following measurements were made for each lizard: SVL tail length (TL) head width (HW) and LL (from the carpus to the elbow). Lizards that were first captured as hatchlings or early yearlings could be accurately aged (in months) and were used in the following analysis. Animals were released at the site of capture after measurements were taken.

Sexual size dimorphism

All lizards for which gender and age could be determined were used in the SSD analysis. For each age class, the overall body size and other proportional measurements were compared between the two sexes. Analysis of variance (ANOVA) was used to examine the SVL difference between male and female lizards of the same age category, while analysis of covariance (ANCOVA) (using SVL as a covariate) was used to examine sex differences in TL, LL, and HW. To determine whether the SSD pattern varied among age classes, ANOVA and ANCOVA (using SVL as a covariate) were used with age and sex as factors and other length characteristics as dependent variables.

Growth rate

Male and female growth in SVL under natural conditions was compared using two approaches. First, for each age category, linear growth rates between two censuses were compared directly. Growth rate was estimated by subtracting initial SVL from final SVL and dividing by elapsed time. Then, the correlation between growth rate and the mean SVL at initial and final capture was examined for each age category. If there was significant correlation, ANCOVA (using mean SVL as a covariate, sex as a factor) was used to detect the difference in growth rate between sexes, otherwise ANOVA was used. Capture intervals less than 15 days and greater than 60 days were not considered.

In the second approach, various growth models were fitted and compared between male and female lizards. We first calculated the size-specific growth rate (SGR) as the growth rate divided by the mean SVL of initial and final capture [18]. We then fitted the SGR and SVL of the two sexes to logistic, Gompertz and von Bertalanffy growth models, as described in Johnston [7]. The logistic model produced the highest value of R 2 from a linear regression of the original data and was chosen as the best model (Table 1). SVL data from accurately aged (in months) lizards were fitted to the best model and the asymptotic length (A) and the characteristic growth rate (k) were estimated and directly compared between the sexes. The SVL of the smallest measured neonate was set as the size at age zero (25.98 mm for both sexes), and absolute time was converted to ‘growth months’ by subtracting the period of winter dormancy (late October to the following late March, about 5 months).

Survivorship

Survivorship was determined by a lizard's continued presence in sequential censuses. When a lizard was absent from a census and was never seen again it was treated as a mortality at the first absence. Short-range emigration was checked by searching for marked individuals in the buffer zone around the quadrat. The survivorships of eggs and the hatching rate were not investigated in this study. The primary sex ratio was assumed to be 1∶1. Time-specific life tables for each sex were established using the estimated age-specific survivorship (lx), mortality rate (qx), and life expectation (ex), following Sun [19].

Statistical analyses

All data were tested for normality and homogeneity of variances and were ln-transformed when necessary to achieve the conditions for using parametric tests. Statistical tests were performed using SPSS 19.0 for Windows. Values are expressed as means ±SE and P<0.05 was considered as statistically significant.

Ethics Statement

Our experimental procedures complied with the current laws on animal welfare and research in China and were specifically approved by the Animal Research Ethics Committee of Lanzhou University. The capturing and tagging of animals were authorized by China's Ministry of Education.


4.9: Sexual dimorphism - Biology

Male (♂) is the sex of an organism that produces the gamete known as sperm, which fuses with the larger female gamete, [1] [2] [3] or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. [4] Most male mammals, including male humans, have a Y chromosome, [5] [6] which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically however, species such as Cymothoa exigua change sex depending on the number of females present in the vicinity. [7]

Male can also be used to refer to gender.

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). [8] [9] The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. [10]

Accordingly, sex is defined across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another. [9] [11] [12]

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants. [ citation needed ]

Symbol

A common symbol used to represent the male sex is the Mars symbol ♂, a circle with an arrow pointing northeast. The Unicode code-point is:

U+2642 ♂ MALE SIGN (HTML &#9794 · &male )

The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is sometimes seen as a stylized representation of the shield and spear of the Roman god. Mars. According to Stearn, however, this derivation is "fanciful" and all the historical evidence favours "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 1588–1683)" that it is derived from θρ, the contraction of a Greek name for the planet Mars, which is Thouros. [13]

Usage

In addition to its meaning in the context of biology, male can also refer to gender [14] or a shape of connectors. [15] [16]

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species have only two sexes (either male or female), [8] [9] [17] hermaphroditic animals, such as worms, have both male and female reproductive organs. [18]

Genetic determination

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including humans, to be XX male or have other karyotypes. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. [19]

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. [20] The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development [21] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development. [22]

The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid. [ citation needed ]

Environmental determination

In some species of reptiles, such as alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. [23] In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. [24]

In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia. [ citation needed ]

In those species with two sexes, males may differ from females in ways other than the production of spermatozoa.

In many insects and fish, the male is smaller than the female.

In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism.

In mammals, including humans, males are typically larger than females. [25]

In humans, males have more body hair and muscle mass. [26]

In birds, the male often exhibits a colorful plumage that attracts females. [27]


Sexual dimorphism in interferon-tau production by in vivo-derived bovine embryos

Interferon-tau (IFN-tau) is an anti-luteolytic factor responsible for preventing regression of the maternal corpus luteum (CL) during early pregnancy of cattle. In vitro-produced (IVP) bovine embryos first produce IFN-tau as blastocysts. In the present study, we have examined whether sexually dimorphic production of IFN-tau, which is observed among IVP blastocysts, also occurs among in vivo-produced blastocysts, and whether this difference between the sexes persists to day 14 when silencing of one of the X-chromosomes in the trophectoderm is complete. Embryos were flushed from cattle that had been superovulated and bred by AI. Blastocysts (63 male, 62 female) recovered between days 8.5 and 9.5 of pregnancy, were cultured individually. No differences were observed between males and females in either their developmental stage or quality at the beginning, during, and at the end of culture. Female embryos produced more IFN-tau than males by 24 hr (mean values, males: 16.6 +/- 3.7, females: 49.4 +/- 9.0 pg per embryo P < 0.05) and 48 hr (male: 189.8 +/- 37.1, female: 410.9 +/- 66.6 pg per embryo P < 0.05). However, the variability in IFN-tau production between individual blastocysts was so great that IFN-tau secretion is unlikely to be of value as a non-invasive means to predict embryo sex. When conceptuses were recovered at day 14, elongating males (n = 25) and females (n = 24) were similar in dimension and did not differ in their IFN-tau production after 4.5 hr (male: 2,550 +/- 607, female: 2,376 +/- 772 ng per conceptus) and 24 hr (male: 12,056 +/- 2,438, female: 8,447 +/- 1,630 ng per conceptus) of culture. Thus, sexual dimorphism in IFN-tau production is observed in both IVP and in vivo-produced expanded blastocysts, but is lost by day 14 of in vivo development.


Sex determination

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. ⎥]

Most animal species that reproduce sexually have only two sexes (either male or female). ⎦] ΐ]

In some species females can coexist with hermaphrodites, a system gynodioecy. ⎥]

Genetic determination

The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y (as opposed to X and X) sex chromosomes. During reproduction, the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The ZW sex-determination system, where males have ZZ (as opposed to ZW) sex chromosomes, is found in birds, reptiles and some insects and other organisms. ⎥]


GROWTH PATTERN, REPRODUCTIVE PERFORMANCE AND SEASONAL SENSITIVITY OF BOVAN NERA AND ISA BROWN PARENT-STOCK CHICKENS IN IBADAN NIGERIA

Parent stocks (PS) of exotic hybrids have contributed immensely to commercial poultry production in Nigeria. Their continued optimal utilization depends on their performance test. Information on performance indices of PS layer breeds in South-West Nigeria is however limited. The growth, reproductive performance and seasonal sensitivity of Bovan Nera (BN) and Isa Brown (IB) hybrids were evaluated.

Secondary data on 24 batches of PS of each of BN and IB kept over a period of 10 years (1999- 2008) in Ajanla Farms, Ibadan were used. Average batch population was 3896 pullets and 600 cockerels at point-of-lay. Records on Body Weight (BW), Age, Hen-Day-Production (HDP), Egg Weight (EWt), Egg fertility (EF), Egg Hatchability (EH), Pullet Day-Old Chicks produced (PDOC) and Hatching Rejects (HR) in four seasons: Early-Wet (EW, April-July) Late-Wet (LW, August-October) Early-Dry (ED, November-January) and Late-Dry (LD, February- March) were obtained. Data were standardized and analysed for growth, Age-at-first-egg (AFE), HDP characteristics, reproduction, seasonal sensitivity, genotype-season interaction using descriptive statistics, ANOVA, correlation and regression (p=0.05).

There was no significant difference in BW (g) and growth rate (g/day) between hybrids: 1724.8±562.8 and 1549.8±543.3 1.4±2.3 and 1.1±1.6 for BN and IB hens, respectively. Effect of seasons on AFE was not significant in both hybrids, but ED and LD seasons delayed AFE. The HDP values (%) recorded for BN (63.2) and IB (72.9) in ED were significantly higher than in other seasons. There were significant differences in EF (80.8 and 88.7%), EH (69.1 and 73.6%), PDOC (32.6 and 36.1%) and EWt (56.2 and 59.9 g) for BN and IB respectively in EW season. EF (86.2 and 89.5%) and EH (73.1 and 73.9%) in LW were highest within hybrids respectively. Phenotypic correlation (r) between Age and Hen Weight, Age and EWt, Hen Weight and EWt, EF and EH, EF and PDOC, and EH and PDOC were 0.78, 0.74, 0.68, 0.73, 0.72 and 0.98 in BN and 0.77, 0.52, 0.53, 0.69, 0.71, and 0.97 in IB respectively. The positive and significant correlation between HR and EWt (r = 0.14 and 0.13), for BN and IB respectively, indicated increase in HR as EWt increased. The environmental performance in body weight of both hybrids was significantly depressed before 10 weeks in cocks and throughout the life cycle of hens, except at 10 to 16 weeks in the BN hen. Performance depression was also observed in HDP (-10.2%), EF (-6.9%) and EH (-14.4%) in IB, and EWt (- 2.9 and -3.2%) in both genotypes respectively over their life-time period. Predictions of BW by 222 Age (R = 0.85, 0.84), EWt by Age-in-production (R = 0.65, 0.65), and PDOC by EH (R = 0.99, 0.95) in both hybrids were significant at 25-75 weeks.

Hen day production, egg fertility, egg hatchability, pullet day-old chicks were higher in Isa Brown than Bovan Nera during the early-dry season. Body weight was higher in the cocks of both hybrids in early-dry and late-dry than in early-wet and late-wet seasons. The sensitivity of Isa Brown was lower than Bovan Nera except in hen weight.

Keywords: Bovan Nera, Chicken growth, Isa Brown

Content Page
Fly Leaf
Title
Abstract
Dedication
Acknowledgement
Certification
Table of Contents

List of Tables
List of Figures
Definitions
Abbreviations

Chapter 2.0 LITERATURE REVIEW

2.1 Definition and background 4

2.2 National poultry population 4

2.3.0 Bovan Nera and ISA Brown strains 5

2.3.1 Origin and popularity 5

2.4.1 Growth of body parts 7

2.4.3 Growth performance in chicken 9

2.5 Stocking density and behavioural pattern 12

2.6 Deep litter system and chicken performance 12

2.7 Management operations in chicken breeding 12

2.8 Feed uptake and feeding 13

2.11 Egg traits in poultry 16

2.12 Egg production cycle 16

2.14 Persistency in egg production 20

2.15 Factors affecting egg production in deep litter flocks 21

2.16.0 Negative influences on egg production 21

2.16.1 Photo-refractoriness 21

2.18 Factors affecting egg size 24

2.19 Nutrition and egg weight 24

2.21 Storage of hatchable fertile eggs 25

2.22 Fertility of incubated chicken eggs 26

2.23 Hatchability of chicken eggs 26

2.24 Day-old chicks’ body weight 27

2.25 Hatchery wastes and disposal 27

2.26 Environment and chicken reproduction 27

2.27 Breeder hen selection and age 28

2.28 Hen testing and comparison parameters 28

2.29 Correlation among morphological traits 29

2.30 Evaluation of chicken flock 29

2.31 Genotype sensitivity 30

2.32 Genotype-environment interaction 31

3.3 Housing and population 34

3.5 Management operations 34

3.6 Seasonal weather conditions of research field 36

3.8 Experimental design 38

3.10 Regression models for growth and egg weight 39

3.11 Seasonal response model 39

3.12 Estimation of parameters 40

3.14 Statistical analysis 43

3.16 Test of hypotheses 43

A. The effect of seasons on growth, productive and reproductive performance Growth pattern of Bovan Nera and ISA Brown

4.1.1 Body weight of breeder cocks 44

4.1.2 Body weight of breeder hens 44

4.1.3 Growth pattern of breeder cocks 44

4.1.4 Growth pattern of breeder hens 45

Early sexual maturity characteristics of Bovan Nera and ISA Brown at first-egg

4.2.1 The effect of seasons on early sexual maturity characteristics at first-egg 50

4.2.3 Body weight of breeder pullets at first-egg 53

4.2.4 Body weight of breeder cockerels at first-egg 53

Full sexual maturity characteristics at peak hen-day production

4.3.1 Age at peak hen-day production 56

4.3.2 Body weight of cocks at peak hen-day production 56

4.3.3 Body weight of pullets at peak hen-day production 60

4.3.4 Hen-day production at peak hen-day production 60

4.3.5 Egg weight at peak hen-day production 63

4.3.6 Eggs set at peak hen-day production 63

4.3.7 Egg fertility at peak hen-day production 63

4.3.8 Egg hatchability at peak hen-day production 67

4.3.9 Pullet day-old chicks hatched at peak hen-day production 67

4.3.10 Hatching rejects at peak hen-day production 70

Productive performance characteristics of Bovan Nera and ISA Brown

4.4.1 Life-time productive performance 72

4.4.4 Persistency of egg production 74

Reproductive performance characteristics of Bovan Nera and ISA Brown

4.5.1 Life-time reproductive performance 76

4.5.2 Life-time percent of eggs set 76

4.5.3 Life-time fertility of eggs set 76

4.5.4 Life-time hatchability of eggs set 80

4.5.5 Life-time pullet day-old chicks hatched 82

4.5.6 Life-time hatching rejects 82

B. The effect of genotype growth pattern and reproductive parameters

4.6.1 Growth performance 87

4.6.2 Sexual dimorphism in body weight 87

4.6.3 Early sexual maturity characteristics 87

4.6.4 Body weight and egg characteristics at full sexual maturity 87

4.6.5 Life-time productive characteristics 88

4.6.6 Life-time reproductive characteristics 88

C. Genotype by season interaction and genotype sensitivity to seasons

4.7 Genotype by season interaction 97

4.8.1 Genotype sensitivity 101

4.8.2 Within-seasons sensitivity 101

4.8.3 Between-seasons sensitivity 102

D. Environmental performance of Bovan Nera and ISA Brown

4.9.1 Environmental performance evaluation 122

4.9.2 Performance depression 122

E. Relationships among growth, productive and reproductive parameters

4.10.1 Relationship among the growth parameters for cocks 128

4.10.2 Relationship among the growth parameters for hens 128

4.10.3 Phenotypic correlation among productive parameters 128

4.10.4 Phenotypic correlation among reproductive parameters 128 4.10.5 Relationship between cock weight and fertility of eggs set 129

4.10.6 Relationship between egg weight and hatchability of eggs set 129

F. Predictive models for growth, productive and reproductive parameters

4.11.1 Body weight and growth 142 4.2.2 Egg weight 142 4.12.3 Fertility and hatchability of eggs set 143

A. The effect of seasons on growth, productive and reproductive performance Growth pattern of Bovan Nera and ISA Brown

5.1.1 Body weight of breeder cocks 148

5.1.2 Body weight of breeder hens 148

5.1.3 Growth pattern of breeder cocks 149

5.1.4 Growth pattern of breeder hens 149

Early sexual maturity characteristics of Bovan Nera and ISA Brown at first-egg

5.2.1 The effect of seasons on early sexual maturity characteristics at first-egg 150

5.2.3 Body weight of breeder pullets at first-egg 150

5.2.4 Body weight of breeder cockerels at first-egg 151

Full sexual maturity characteristics at peak hen-day production

5.3.1 Age at peak hen-day production 152

5.3.2 Body weight of cocks at peak hen-day production 152

5.3.3 Body weight of pullets at peak hen-day production 153

5.3.4 Hen-day production at the peak of production 153

5.3.5 Egg weight at peak hen-day production 153

5.3.6 Eggs set at peak hen-day production 154

5.3.7 Fertility of eggs set at peak hen-day production 154

5.3.8 Hatchability of eggs set at peak hen-day production 154

5.3.9 Pullet day-old chicks hatched at peak hen-day production 155

5.3.10 Hatching rejects at peak hen-day production 155

Productive performance characteristics of Bovan Nera and ISA Brown

5.4.1 Life-time productive performance 156

5.4.2 Life-time hen-day production 156

5.4.3 Life-time egg weight 157

5.4.4 Persistency of egg production 157

Reproductive performance characteristics of Bovan Nera and ISA Brown

5.5.1 The effect of seasons on reproductive parameters 159

5.5.2 Life-time percent of eggs set 159

5.5.3 Life-time fertility of eggs set 159

5.5.4 Life-time hatchability of eggs set 160

5.5.5 Life-time pullet day-old chicks hatched 161

5.5.6 Life-time hatching rejects 161

B. The effect of genotype on growth pattern and reproductive parameters

5.6.2 Sexual dimorphism in body weight 162

5.6.3 Early sexual maturity characteristics at first-egg 163

5.6.4 Body weight and egg characteristics at peak hen-day production 163

5.6.5 Life-time productive performance 164

5.6.6 Life-time reproductive performance 165

C. Genotype by season interaction and genotype sensitivity to seasons

5.7.1 Genotype by season interaction 165

5.7.2 Implication for egg production and pullet day-old chicks hatched 167

5.8.0 Genotype sensitivity to seasons 168

5.8.1 Within-seasons sensitivity 168

5.8.2 Between-seasons sensitivity 170

D. Environmental performance of Bovan Nera and ISA Brown

5.9.1 Environmental performance evaluation 171

5.9.2 Performance depression 172

E. Relationships among growth, productive and reproductive parameters

5.10.1 Phenotypic correlation among the growth parameters 174

5.10.2 Phenotypic correlation among the productive parameters 175

5.10.3 Phenotypic correlation among the reproductive parameters 175

5.10.5 Relationship between cock weight and fertility of eggs set 176

5.10.6 Relationship between egg weight and hatchability of eggs set 177

F. Predictive models for growth, productive and reproductive parameters

4.11.1 Body weight and growth 178 4.12.2 Egg weight and hen-day production 179

4.12.3 Fertility and hatchability of eggs set 180

Chapter 6.0 CONCLUSION AND RECOMMENDATIONS

6.4 Areas for further research 185

7.2.1 Cock body weight depression of Bovan Nera and ISA Brown in hot-humid Ibadan environment 205

7.2.2 Hen body weight depression of Bovan Nera and ISA Brown in hot-humid Ibadan environment 206

7.2.3 Depression of age, hen-day production and egg weight of Bovan Nera and ISA Brown in hot-humid Ibadan environment 207

7.2.4 Depression of egg fertility and hatchability of Bovan Nera and ISA Brown in the hot-humid Ibadan environment 208

7.2.5 Seasonal stocking pattern, recommended stocking dates and onset of egg-lay in Bovan Nera and ISA Brown hybrids 209

7.2.6 Technical data on mean body weight, production and reproduction data on Bovan Nera Parent-stock flock raised on deep-litter system in the hot – humid Ibadan, South-West Nigeria 210

7.2.7 Technical data on mean body weight, production and reproduction data on ISA Brown Parent-stock flock raised on deep-litter system in the hot - humid Ibadan South-West Nigeria


Sexual Dimorphism in Zooplankton (Copepoda, Cladocera, and Rotifera)

In this review we consider sexual dimorphism in copepods, cladocerans, and rotifers. All three groups may be common components of freshwater and sometimes estuarine zooplankton communities, but only the copepods are generally found in marine zooplankton communities. To varying degrees, these three groups exhibit important differences between the sexes in size and in other secondary sexual characteristics that are not directly related to reproduc­ tion. For each group, we summarize the life cycle describe genetic, morpholo­ gical, physiological, and behavioral differences between the sexes and then discuss the evolution of these differences and their ecological implications. COPEPODA Life Cycle The planktonic copepods of marine and inland waters are composed almost entirely of individuals from two of the three free-living orders 0f the subclass Copepoda. The Calanoida are almost entirely planktonic. The Cyclopoida are primarily littoral and benthic but do include several widespread and abundant planktonic species. The few species of Harpacticoida found among the plank­ ton tend to be either vagabonds accidentally washed out from shore or indi- 0066-4162/83/1 120-0001$02.00 GILBERT & WILLIAMSON viduals that remain very closely associated with detritus, algae, or other substrates (151, 224). (32, 62), The life cycles of copepods are fundamentally different from

Journal

Annual Review of Ecology, Evolution, and Systematics &ndash Annual Reviews


Sexual dimorphism in the neurophil of the preoptic area of the rat and its dependence on neonatal androgen

The stria terminalis sends fibres to a well circumscribed zone in the dorsal part of the preoptic area. This ‘strial part of the preoptic area’ contains cells with beaded, spine-poor dendrites arranged horizontally so as to intersect at right angles with the strial axons it also receives aminergic fibres from the reportedly noradrenergic plexus in the bed nucleus of the stria terminalis. The strial part of the preoptic area is separated from the ventral part of the strial bed nucleus by a compact mass of cells (the ‘round nucleus’) which, unlike the other two areas, does not receive either aminergic fibres or synapses from the strial axons.

The incidences of various types of synapses have been counted in the neuropil of the strial part of the preoptic area and in the region lying between the ventromedial and arcuate hypothalamic nuclei. Synapses on dendritic shafts outnumber those on dendritic spines in the ventromedial nucleus, and to an even greater degree in the preoptic area. In both regions fibres of amygdaloid origin passing through the stria terminalis establish synapses (identified by the electron dense reaction of orthograde degeneration two days after axotomy) on both dendritic shafts and (especially in the ventromedial nucleus) on spines.

There is no sexual dimorphism in the incidences of the shaft synapses or any of the synapses of amygdaloid origin in the preoptic area, and none in any category of synapse in the ventromedial nucleus. However, in the normal females the number of non-amygdaloid synapses on dendritic spines in the preoptic area is higher than in the male. The suggestion that this difference could be related to the ability of the female to maintain a cyclic pattern of gonadotrophin release and/or behavioural oestrus is supported by published work implicating the preoptic area in the control of ovulation and mating behaviour.

Castration of the male within 12 h of birth (but not at 7 days of age) causes an increase to the female level in the number of spine synapses and permits the development of a cyclic pattern of gonadotrophin release and the ability to show a progesterone facilitated increase in receptivity. Conversely, females treated on day 4 (but not on day 16) with 1.25 mg of testosterone propionate have a low number of spine synapses (in the male range) this treatment also abolishes the cyclic pattern of gonadotrophin release and the progesterone facilitated increase in receptivity.


Watch the video: Men and Women Are Different.. But How Different? Sexual Dimorphism Vs. Monomorphism in Humans (October 2022).