Effects of parity on pelvic size and shape dimorphism in Mus

The pelvis is a sexually dimorphic structure and although the causes of that dimorphism have long been studied, relatively little is known regarding the effects of partuitive events on the magnitude of that dimorphism. Here, we use a sample of Mus musculus domesticus to contrast dimorphism in body length and os coxae size and shape between males and parous and nulliparous females. We also test for correlations between relative litter size (L/M) and relative offspring size (O/M) with body length and os coxae size and shape in parous females. Males had greater body length than nulliparous females but were not different from parous females. Females as a whole had the largest os coxae, with parous females having the largest and males the smallest. Os coxae shape was also significantly different between groups and was most divergent between parous females and males than between nulliparous females and males. Os coxae shape differences between females are associated with differences in body length between females and O/M is correlated with os coxae shape in parous females such that females with the largest offspring have the most divergent shapes along the relative warp one axis. Pelvic shape differences between males and females were consistent with previous findings in other taxa which identify the pubo‐ischial complex as the primary region of dimorphism. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Sexual dimorphism and developmental patterns in the external morphology of the vaquita,Phocoena sinus

A total of 56 vaquitas (Phocoena sinus) were examined to evaluate their sexual dimorphism and isometric and/or allometric growth in 35 external characteristics. Absolute and relative (to total length) measurements and growth rates were compared between sexually immature and mature females and males. T‐tests and analysis of variance (ANOVA) and covariance (ANCOVA) were used to evaluate sexual dimorphism. Sexual dimorphism in the vaquita was detected in the total length, head region (from blowhole to tip of upper jaw), anterior section of the body (from dorsal fin to tip of upper jaw), dorsal fin and the genital and anal regions. Fluke width is relatively larger in mature males than immature males, but in females this relative metric does not change during their development. In addition, males present a higher dorsal fin. These somatic changes are probably related to the swimming capacity (speed, agility, maneuvering) during the breeding season and/or foraging activities. A linear model of growth was used to determine possible proportional changes with respect to total body length through the development of 33 external characteristics. The anterior region of the body and the flippers were relatively larger in immature individuals than in mature ones.     

Sexual Dimorphism in the Pelvis of <Emphasis Type="Italic">Microcebus</Emphasis>

Pelvic sexual dimorphism occurs in many anthropoid species and is often attributed to obstetric selection on female pelvic morphology. Few studies of pelvic dimorphism have included strepsirrhine taxa, which typically have relatively smaller infants than those of anthropoids. Because smaller female primates give birth to relatively larger infants, it is possible that the pelves of Microcebus, the smallest extant primate genus, will show some evidence of selection on obstetric adequacy. A comparison of adult female and neonatal body masses indicates that individual neonatal Microcebus are relatively large compared to adult female body mass, even though members of the taxon frequently produce twins. I examined variation in the bony pelvis within a sample of Microcebus. I measured specimens from a single locality, which probably represent 1 population. I measured 8 pelvic and 3 femoral variables to investigate skeletal size and pelvic size and shape dimorphism. Females significantly exceed males in absolute values of sacral width, pelvic height, pubic length, and distances from the pubic symphysis to the ischial tuberosity and points on the sacrum. Measurements of the femur are not significantly greater in females, suggesting that the pelvic differences are not due to skeletal size dimorphism. Significant pelvic shape or ratio differences, calculated via the geometric mean of 5 variables as the denominator, included greater relative pubic length and sacral width in females. Hence selection for obstetric adequacy may occur in the extremely small-bodied Microcebus.     

Sexual size dimorphism in Darevskia raddei (Sauria: Lacertidae) from northwestern Iran

We examined sexual size dimorphism of the rock-dwelling lizard Darevskia raddei (Boettger, 1892) with the help of 30 specimens that were provided from various sources. Eleven metric and seven meristic features were examined. Seven characters (gulars, length of basal tail, femoral pores, length of head, width of head, length of fore limb and length of hind limb) were identified as dimorphic between the two sexes. Some of these characters have important roles in copulation for males, especially the hind limb and the tail base. The number of femoral pores is important in the release of signal components because females release these components to attract males during the mating season. The length of the hind limb as locomotor performance plays an important role during mating, so that the male can grasp the female and adopt the correct position during copulation.     

Costal process of the first sacral vertebra: sexual dimorphism and obstetrical adaptation

The human sacrum is sexually dimorphic, with males being larger than females in most dimensions. Previous studies, though, suggest that females may have a longer costal process of the first sacral vertebra (S1) than males. However, these studies neither quantified nor tested statistically the costal process of S1. This study compares S1 with the five lumbar vertebrae (L1 to L5) for a number of metric dimensions, including costal process length. Four issues are addressed, the: 1) hypothesis that females have a longer costal process of S1 than males; 2)hypothesis that homologous structures (i.e., costal processes of L1 to S1) differ in their direction of sexual dimorphism; 3) importance of the costal process of S1 to the obstetrical capacity of the pelvis; and 4) evolution of sexual dimorphism in costal process length of S1. One hundred ninety-seven individuals, including males and females of American blacks and whites, from the Hamann-Todd and Terry Collections were studied. Results show that males are significantly larger than females for most vertebral measurements, except that females have a significantly longer costal process of S1 than males. Costal process length of S1 is positively correlated with the transverse diameter and circumference of the pelvic inlet. The magnitude of sexual dimorphism in costal process length of S1 ranks this measure among the most highly dimorphic of the pelvis. Compared with the humans in this study, australopithecines have a relatively long costal process of S1, but their broad sacrum was not associated with obstetrical imperatives.     

Sexual dimorphism and female reproductive cycle in the scincid lizard Trachylepis vittata (Olivier, 1804) in Lebanon (Reptilia: Scincidae)

Sexual dimorphism and the female reproductive cycle were studied in a population of the viviparous lizard Trachylepis vittata at 2000 m a.s.l. on Mount Sannine, Lebanon. Females have larger body sizes than males and males have relatively larger heads than females. Females reach maturity at 56 mm snout-vent length. They spend at least six months in hibernation, from October to March. Adult females emerge from hibernation in April. Fertilization occurs mid-May and gestation lasts for 8-10 weeks. All females collected on the same date had embryos at the same embryonic developmental stage. Females produced 1-4 embryos. There is a significant positive relationship between female body size and number of embryos. Parturition lasts for two weeks and new-borns achieve adult size within about ten months.     

Sexual dimorphism in snake tail length: sexual selection,natural selection,or morphological constraint?

Male snakes typically have longer tails relative to body length than females, but the extent of this dimorphism varies among species. Three hypotheses have been suggested to explain tail dimorphism. The Morphological Constraint Hypothesis proposes that males have relatively longer tails to accommodate hemipenes and retractor muscles. The Female Reproductive Output Hypothesis proposes that females have relatively shorter tails as a secondary result of natural selection for increased reproductive capacity. The Male Mating Ability Hypothesis proposes that sexual selection favours relatively longer tails in males during courtship. These hypotheses make different predictions about the relationships among tail length, body size, male reproductive morphology, female reproductive output, mode of reproduction, and male mating behaviour among and within taxa. Predictions were tested using published data for 56 genera in the family Colubridae and original data for the water snake, Nerodia sipedon. Tail length dimorphism was more male-biased in tam having relatively short tails (r=–0.52, P < 0.001), hemipenes and retractor muscles occupied a greater proportion of the tail in taxa having relatively short tails (r=– 0.71, P < 0.00l and r=– 0.66, P = 0.001, respectively), and tail length dimorphism was more male-biased in taxa in which body size dimorphism was more female-biased (r=– 0.60, P < 0.001). These results support both the Morphological Constraint Hypotheses and the Female Reproductive Output Hypothesis. However, tests of other predictions, including those regarding patterns within N. sipedon , failed to support any of the three hypotheses. Comparisons among taxa suggest several species in which further tests of these hypotheses would be especially appropriate.     

First report of wing dimorphism in the genus Orthomus (Coleoptera: Carabidae)

Wing polymorphism has been reported for several carabid beetles. Traditionally, a great number of ecological and evolutionary studies have focused on this peculiarity, which has implications on dispersal power. Research based on Orthomus berytensis specimens from two sampling areas of Tenerife (Canary Islands, Spain) has shown that this species exhibits a wing dimorphism, instead of being brachypterous. This makes O. berytensis the first Orthomus wing dimorphic species to date. Statistical differences in macropterous percentage between both sexes and localities were found. Also, a sexual dimorphism in elytra length and width was found, both being higher in females.     

Sexual differences in head form and diet in a population of Mexican lance‐headed rattlesnakes,Crotalus polystictus

Sexual dimorphism of phenotypic traits associated with resource use is common in animals, and may result from niche divergence between sexes. Snakes have become widely used in studies of the ecological basis of sexual dimorphism because they are gape‐limited predators and their head morphology is likely to be a direct indicator of the size and shape of prey consumed. We examined sexual dimorphism of body size and head morphology, as well as sexual differences in diet, in a population of Mexican lance‐headed rattlesnakes, Crotalus polystictus, from the State of México, Mexico. The maximum snout–vent length of males was greater than that of females by 21%. Males had relatively larger heads, and differed from females in head shape after removing the effects of head size. In addition, male rattlesnakes showed positive allometry in head shape: head width was amplified, whereas snout length was truncated with increased head size. By contrast, our data did not provide clear evidence of allometry in head shape of females. Adults of both males and females ate predominately mice and voles; however, males also consumed a greater proportion of larger mammalian species, and fewer small prey species. The differences in diet correspond with dimorphism in head morphology, and provide evidence of intersexual niche divergence in the study population. However, because the sexes overlapped greatly in diet, we hypothesize that diet and head dimorphisms in C. polystictus are likely related to different selection pressures in each sex arising from pre‐existing body size differences rather than from character displacement for reducing intersexual competition. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 633–640.     

Cranial morphology and adaptations in Eocene Adapidae. I. Sexual dimorphism in Adapis magnus and Adapis parisiensis

Adapis is one of the best known lemuriform fossil primates. Quantitative analysis of all well-preserved crania of Adapis magnus (n = 8) and Adapis parisiensis (n = 12) together with maxillary and mandibular dentitions preserving canines corroborates Stehlin's hypothesis that Adapis was sexually dimorphic. Males are from 13% to 16% larger than females in cranial length, corresponding to a weight dimorphism estimated at 44% to 56%, and have relatively broader skulls with more prominent sagittal and nuchal crests. Canine dimorphism ranges from 13% to 19%, which is equal to or only slightly greater than that expected as a result of body size dimorphism (i.e., relative canine dimorphism is slight or nonexistent). By comparison with living primates, the observed body size dimorphism in Adapis implies a polygynous breeding system. Cebus apella is a diurnal arboreal living primate with moderate body size dimorphism and slight relative canine dimorphism and one can speculate that Adapis lived in polygynous multimale troops of moderate size like those of C. appella. Adapis extends the geological history of sexual dimorphism and polygyny in primates back to the Eocene. Extant lemuriform primates are generally not dimorphic or polygynous and they clearly do not adequately represent the range of social adaptations present in Eocene primates. The evolutionary lineage from Adapis magnus to Adapis parisiensis exhibits reduction in body size and in relative canine size, and phyletic dwarfing in Adapis is possibly an adaptive response to increasing climatic seasonality and environmental instability in the late Eocene and early Oligocene.     

Ontogeny and sexual dimorphism in a captive population of juvenile striped skunks <Emphasis Type="Italic">Mephitis mephitis</Emphasis>

Three main hypotheses can explain the origin of the sexual size dimorphism: (1) the birth-size hypothesis, which states that birth size of males is larger than that of females; (2) the growth-rate hypothesis, which states that males grow faster than females; (3) the growth-length hypothesis, which states that males grow for a longer period of time than females. We examined the factors that may contribute to sexual size dimorphism with growth data of striped skunks Mephitis mephitis Schreber, 1776 held in captivity in Manitoba (Canada), from 7 to 72 days of age. At seven days of age, the mass of male skunks (mean = 79.7 g ± 13.9 SE, n = 37) was significantly larger than that of females (mean = 71.2 g ± 15.0 SE, n = 35) but the head and body length was not statistically different between males (mean = 110.3 mm ± 8.0 SE, n = 37) and females (mean = 95.3 mm ± 7.4 SE, n = 35). There was no difference in growth rate for mass or for length between sexes. We were not able to test for a difference in growth length between sexes. Our results suggest that mass dimorphism occurs early in life.     

Evolution of Sexual Dimorphism in the Number of Tail Vertebrae in Salamanders: Comparing Multiple Hypotheses

The evolution of sexual dimorphism is an important topic of evolutionary biology, but few studies have investigated the determinants of sexual dimorphism over broad phylogenetic scales. The number of vertebrae is a discrete character influencing multiple traits of individuals, and is particularly suitable to analyze processes determining morphological variation. We evaluated the support of multiple hypotheses concerning evolutionary processes that may cause sexual dimorphism in the number of caudal vertebrae in Urodela (tailed amphibians). We obtained counts of caudal vertebrae from >2,000 individuals representing 27 species of salamanders and newts from Europe and the Near East, and integrated these data with a molecular phylogeny and multiple information on species natural history. Per each species, we estimated sexual dimorphism in caudal vertebrae number. We then used phylogenetic least squares to relate this sexual dimorphism to natural history features (courtship complexity, body size dimorphism, sexual ornamentation, aquatic phenology) representing alternative hypotheses on processes that may explain sexual dimorphism. In 18 % of species, males had significantly more caudal vertebrae than females, while in no species did females have significantly more caudal vertebrae. Dimorphism was highest in species where males have more complex courtship behaviours, while the support of other candidate mechanisms was weak. In many species, males use the tail during courtship displays, and sexual selection probably favours tails with more vertebrae. Dimorphism for the number of tail vertebrae was unrelated to other forms of dimorphism, such as sexual ornamentation or body size differences. Multiple sexually dimorphic features may evolve independently because of the interplay between sexual selection, fecundity and natural selection.     

Reproduction and sexual dimorphism in the viviparous lizard Sceloporus palaciosi (Squamata: Phrynosomatidae) from the Trans‐Mexican Volcanic Belt,Mexico

In this study, sexual dimorphism, reproductive cycles, litter size and offspring size of a population of the little‐known species Sceloporus palaciosi in central Mexico were analysed. Significant male‐biased sexual size dimorphism was recorded in snout–vent length (SVL), head length, head width, forearm length and tibia length. Both sexes showed asynchronous reproductive cycles, and males reached sexual maturity at a smaller SVL (33 mm) than females (37 mm). Testes volumes were small from January to February, testicular recrudescence began from March to June, and decreased in July, but increased again in August and September, followed by a second decrease from October to December. In females, vitellogenesis began from May until ovulation in December. Embryonic development extended from November to March, and a small number of females carried embryos through July. Mean litter size was 4.0 and was positively correlated with female SVL. The length of the reproductive period in S. palaciosi recorded in this study is longer than that recorded for other populations in other parts of this species range. Further studies are needed to clarify reproductive cycles in the other isolated populations of S. palaciosi, and then extended to other species and chromosome races in the Sceloporus grammicus complex.     

Pairing and insemination patterns in a giant weta (Deinacrida rugosa: Orthoptera; Anostostomatidae)

Positive size assortative mating can arise if either one or both sexes prefer bigger mates or if the success of larger males in contests for larger females leaves smaller males to mate with smaller females. Moreover, body size could not only influence pairing patterns before copulation but also the covariance between female size and size of ejaculate (number of spermatophores) transferred to a mate. In this field study, we examine the pre-copulatory mate choice, as well as insemination, patterns in the Cook Strait giant weta (Deinacrida rugosa). D. rugosa is a large orthopteran insect that exhibits strong female-biased sexual dimorphism, with females being nearly twice as heavy as males. Contrary to the general expectation of male preference for large females in insects with female-biased size dimorphism, we found only weak support for positive size assortative mating based on size (tibia length). Interestingly, although there was no correlation between male body size and the number of spermatophores transferred, we did find that males pass more spermatophores to lighter females. This pattern of sperm transfer does not appear to be a consequence of those males that mate heavier females being sperm depleted. Instead, males may provide lighter females with more spermatophores perhaps because these females pose less of a sperm competition risk to mates.     

Signalling fitness: larger males sire more offspring. Studies of the stalk-eyed fly Cyrtodiopsis whitei (Diopsidae,Diptera)

Some species of stalk-eyed flies (Diopsidae, Diptera) have a sexual dimorphism of eyespan. For example, Cyrtodiopsis whitei males have much longer eyestalks than females of equal body length. Expression of this trait increases with the bearers' size. The slope of the log-log regression line eyespan versus body length is close to two in males, while in females it is roughly one. Behavioural experiments suggest that male eyespan signals quantitatively a male's strength or attractiveness to a competitor or mate. We used 3 pure strains of C. Whitei, which were distinguished by their different phosphoglucomutase allele outfit. We compared the reproductive success of males of different sizes and found the number of offspring to be directly proportional to body length. Thus eyespan, rising with the square of body length, provides an exaggerated and highly conclusive signal in the advertisement of fitness.     

When do meadow vipers (Vipera ursinii) become sexually dimorphic? – ontogenetic patterns of sexual size dimorphisms

Contrary to an increasing number of papers that document sexual dimorphism in size (and/or shape) in adults, studies dealing with sex differences in newborn and juvenile snakes are surprisingly scarce. Data about ontogenetic shifts in sexual dimorphism are generally lacking and hence, it is unclear whether sex differences are set at birth or arise post‐natally. In this study, we analyzed patterns of sexual dimorphism in body size, head dimensions and tail length (TL) among newborn, subadult and adult meadow vipers (Vipera ursinii) from the Bjelasica Mt. in Montenegro. Patterns of sexual size dimorphisms differed among traits. There was no significant difference in head dimension of males and females, but adult snakes were sexually dimorphic in body size. Sexual differences in TL were evident since birth but changed in degree throughout ontogeny. Neonate meadow vipers presented highly significant inter‐litter variation in the sexual dimorphism of all traits we have measured. Such family effects may have an important influence on extent of inter‐sexual differences in snakes and should be included in analyses of sexual dimorphism.     

Sexual dimorphism in clonal growth forms and ramet distribution patterns in <Emphasis Type="Italic">Rumex acetosella</Emphasis> (Polygonaceae)

We investigated clonal traits in the dioecious herb Rumex acetosella to characterize sexual dimorphism in clonal forms and to correlate below-ground clonal patterns and above-ground ramet distributions. We recorded creeping root length, branching patterns, ramet and clump (caespitose ramets from the same position on the root) sprouting patterns, and biomass allocations in three females and males. We also estimated the patch size of flowering ramets within a quadrat. No sexual dimorphism was detected in the frequencies of branches and flowering ramets per root length. Male plants allocated proportionally more biomass to below-ground organs. Total root length did not differ between the sexes. Females sprouted more clumps with fewer flowering ramets per root length than males, which sprouted fewer clumps with more flowering ramets, which meant that clump sprouting patterns were phalanx-like in females and guerrilla-like in males. Flowering ramets were aggregately distributed in both females and males and patch sizes were similar between sexes, indicating that the spreader propagations were not found in the guerrilla-like males. We assumed that sexual dimorphism occurred in response to physiological integration for higher reproductive effort in females.     

The ontogeny of cranial sexual dimorphism in two old world monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae)

Allometric and heterochronic approaches to sexual dimorphism have contributed much to our understanding of the evolutionary morphology of the primate skull and dentition. To date, however, extensive studies of sexual dimorphism have been carried out only on the great apes and a few cercopithecine monkeys. To fill this gap, representative dimensions of the skull were collected among ontogenetic series of two dimorphic Old World monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae). The ontogeny of cranial sexual dimorphism was evaluated with least-squares bivariate regression, analysis of covariance (ANCOVA), and analysis of variance (ANOVA). Results indicate that within each species the sexes typically exhibit nonsignificant differences in ANCOVAs of ontogenetic trajectories, except for bivariate comparisons with bicanine breadth. AmongMacaca fascicularis, ANOVAs between males and females of common dental ages show that adult, and frequently subadult, males are significantly larger than females, i.e., sexual dimorphism develops via time and rate hypermorphosis (males primarily grow for a longer time period as well as faster). AmongNasalis larvatus, however, comparisons between males and females of common dental ages indicate that only adult males are significantly larger than females, i.e., sexual dimorphism develops primarily via time hypermorphosis (males grow for a longer time period). Within both species, females appear to exhibit an early growth spurt at dental age 2; that is, many cranial measures for females tend to be larger than those for males. Measures of the circumorbital region (e.g., browridge height), body weight, and bicanine breadth exhibit typically the highest sexual dimorphism ratios. The fact that postcanine toothrow length and neurocranial volume (less so inNasalis) demonstrate very low dimorphism ratios generally supports assertions that postnatal systemic growth (and associated selective pressures thereon) exerts a greater influence on facial, but not neural, dental, or orbital, development (Cochard, 1985, 1987; Shea, 1985a,b, 1986; Shea and Gomez, 1988; Sheaet al., 1990). Additional consideration of ontogenetic differences between species generally supports previous functional interpretations of subfamilial differences in cranial form related to agonistic displays in cercopithecine monkeys (Ravosa, 1990).     

Sexual dimorphism in leg length among orb-weaving spiders: a possible role for sexual cannibalism

The degree and direction of sexual dimorphism across different species is commonly attributed to differences in the selection pressures acting on males and females. The extent of these differences is especially apparent in species that practise sexual cannibalism, where the female attempts to capture and eat a courting male. Here, we investigate the relationship between sexual dimorphism in size and leg length, sexual cannibalism and courtship behaviour in three taxonomic groups of orb-weaving spiders, using morphological data from 249 species in 36 genera. Females are larger than males in all three taxonomic groups, and males have relatively longer legs than females in both the Araneinae and Tetragnathidae. Across genera within each taxonomic group, male body size is positively correlated with both female body size and male leg length, and female body size is positively correlated with female leg length. Sexual size dimorphism is negatively correlated with relative male leg length within the Araneinae, but not within either the Tetragnathidae or the Gasteracanthinae. There was no negative correlation between sexual size dimorphism and relative female leg length in any taxonomic group. We argue that the relationship between sexual size dimorphism and relative male leg length within the Araneinae may be the result of selection imposed by sexual cannibalism by females.     

Sexual dimorphism in relative sacral breadth among catarrhine primates

As the sacrum contributes to the size and shape of the birth canal, the sexually dimorphic sacrum of humans is frequently interpreted within obstetric contexts. However, while the human sacrum has been extensively studied, comparatively little is known about sacral morphology in nonhuman primates. Thus, it remains unclear whether sacral sexual dimorphism exists in other primates, and whether potential dimorphism is primarily related to obstetrics or other factors such as body size dimorphism. In this study, sacra of Homo sapiens, Hylobates lar, Nasalis larvatus, Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, and Pan paniscus were evaluated for sexual dimorphism in relative sacral breadth (i.e., the ratio of overall sacral breadth to first sacral vertebral body breadth). Homo sapiens, H. lar, N. larvatus, and G. gorilla exhibit dimorphism in this ratio. Of these, the first three species have large cephalopelvic proportions, whereas G. gorilla has small cephalopelvic proportions. P. pygmaeus, P. troglodytes, and P. paniscus, which all have small cephalopelvic proportions, were not dimorphic for relative sacral breadth. We argue that among species with large cephalopelvic proportions, wide sacral alae in females facilitate birth by increasing the pelvic inlet's transverse diameter. However, given the small cephalopelvic proportions among gorillas, an obstetric basis for dimorphism in relative sacral breadth appears unlikely. This raises the possibility that sacral dimorphism in gorillas is attributable to selection for relatively narrow sacra in males rather than relatively broad sacra in females. Accordingly, these results have implications for interpreting pelvic dimorphism among fossil primates, including hominins. Am J Phys Anthropol 152:435–446, 2013. © 2013 Wiley Periodicals, Inc.