Sexual dimorphism in the Caspian Pond Turtle, Mauremys caspica (original) (raw)
Related papers
2017
The Caspian pond turtle, Mauremyscaspica, is a terrapin belonging to family Geoemydidae. Totally 130 specimens (67 males and 63 females) were collected manually and by net from different aquatic habitats in Golestan Province from 2016 through 2017. Morphometric characteristics such as length were measured using digital caliper and weight by electronic weighting scale. Skin of this turtle was dark olive green in color and had rows of longitudinal yellow stripes around the head and neck. Their carapace was relatively flat, the bridges between the dorsal and ventral shells were bony, and the ends of anal scutes were found to be pointed. Fingers and toes had swimming membranes. Sexes were identified using the location of vent on the tail. Sex ratios of males to females were nearly 1:1. The maximum straight carapace length (SCL2) was 80.66- 230.16 (156.72 ± 42.93) and 56.96 - 236.84 (147.02 ± 50.76) in males and females respectively. Ratios of SCL2 to maximum plastron length (PL2) were f...
An allometry study of Caspian pond turtle (Mauremys caspica) in Golestan province, Iran
Caspian pond turtle, Mauremys caspica shows allometric growth and sexual dimorphism in the shell. Differences in allometric growth produce sexually dimorphic adults. Our results revealed that females are smaller than males that may be related to the risk of the predation, desiccation, and thermal stress. Allometric changes in shape of the shells are different between males and females. In females shape related characters such as plastral length (Pl1) and plastral fore and hind lobe width (PFLW, PHLW), gular, pectoral, abdominal and anal seam length (GSL, PSL, AbSL, AnSL) which represent width of plastron and plastral length proportionally change with size (related to SCL2 as index of size). The most remarkable changes related to size are right and left bridge length (RBr, LBr) in females but these changes have not effect on shell shape. For males character TL2 changes dramatically related to size (SCL2). Sexual dimorphism of the shell was also evident. ANCOVA indicated that the regression slopes of males and females differed significantly (p> 0.000) in 15 of the 24 characters examined.
Ecological, evolutionary, and allometric patterns of sexual size dimorphism in turtles
Macroevolutionary patterns of sexual size dimorphism (SSD) indicate how sexual selection, natural selection, and genetic and developmental constraints mold sex differences in body size. One putative pattern, known as Rensch's rule, posits that, among species with female-larger SSD, the relative degree of SSD declines with species' body size, whereas, among male-larger SSD species, relative SSD increases with size. Using a dataset of 196 chelonian species from all fourteen families, we investigated the correlation in body size evolution between male and female Chelonia and the validity of Rensch's rule for the taxon and within its major clades. We conclude that male-female correlations in body size evolution are high, although these correlations differ among chelonian families. Overall, SSD scales isometrically with body size; Rensch's rule is valid for only one family, Testudinidae (tortoises). Because macroevolutionary patterns of SSD can vary markedly among clades, even in a taxon as morphologically conservative as Testudines, one must guard against inappropriately pooling clades in comparative studies of SSD. The results of the present study also indicate that regression models that assume the x-variable (e.g. male body size) is measured without statistical error, although frequently reported, will result in erroneous conclusions about phylogenetic trends in sexual size dimorphism.
Geographic Variation in Sexual Size Dimorphism in Painted Turtles (Chrysemys picta)
Journal of Herpetology, 2010
Geographic variation in body size may reflect adaptations to local environments, and sexual size dimorphism (SSD) arises from ultimate and proximate factors acting differently on males and females in those environments. The Painted Turtle (Chrysemys picta) is a wide-ranging North American freshwater turtle species with known female-biased SSD. We hypothesized that, in more seasonal environments, the disparity between adult female and male body size would be more pronounced (i.e., the sexual dimorphism index [SDI, female body size/male body size] would be higher) than in more moderate environments because selective pressures on females to maximize reproductive output would result in relatively larger body sizes (fecundity advantage hypothesis) in extreme environments. We predicted that the SDI would be higher in populations at northern latitudes and middle longitudes than in southern and coastal populations. We conducted linear and nonlinear regression analyses using data from the literature and museum records, extrapolated data, and unpublished data on adult male and female carapace and plastron lengths from 65 locations. In contrast to our prediction, SDI decreased with increasing latitude. With respect to longitude, the trend supported our prediction in that the SDI was slightly higher for interior populations and lower for coastal populations; however, the relationship was not significant. Future research should examine sex differences in carapace height and body volume which may more directly reflect selective pressures on female fecundity than straight-line shell lengths.
Biological Journal of the Linnean Society, 2014
The attainment of sexual maturity has been shown to affect measures of sexual size dimorphism (SSD) and adult sex ratios in several groups of vertebrates. Using data for turtles, we tested the model that sex ratios are expected to be male-biased when females are larger than males and female-biased when males are larger than females because of the relationship of each with the attainment of maturity. Our model is based on the premise that the earlier-maturing sex remains smaller, on average throughout life, and predominates numerically unless the sexes are strongly affected by differential mortality, differential emigration, and immigration, or biased primary sex ratios. Based on data for 24 species in seven families, SSD and sex ratios were significantly negatively correlated for most analyses, even after the effect of phylogenetic bias was removed. The analyses provide support for the model that SSD and adult sex ratios are correlated in turtles as a result of simultaneous correlation of each with sexual differences in attainment of maturity (bimaturism). Environmental sex determination provides a possible mechanism for the phenomenon in turtles and some other organisms.
Authorea
Turtles have been prominent subjects of analyses of sexual size dimorphism (SSD) owing to their mating system and habitat diversity. In prior studies, marine turtles were grouped with non-marine aquatic turtles (NMAT). This is odd because it is well-established that the marine environment imposes a distinct selective milieu on body form of vagile vertebrates, driven by convergent adaptations for energy-efficient propulsion and drag reduction. We generated a comprehensive database of adult marine turtle body size (38,569 observations across all species), which we then used to evaluate both the magnitude of SSD in marine turtles and how it compares to SSD in NMAT. We find that marine turtles are not sexually size dimorphic, whereas NMAT typically exhibit female-biased SSD. We argue that the reason for this difference is the sustained long-distance swimming that characterises marine turtle ecology, which entails significant energetic costs incurred by both sexes. Hence, the ability of either sex to allocate proportionately more to growth than the other is likely constrained, meaning that sexual differences in growth and resultant body size are not possible. Consequently, lumping marine turtles with NMAT dilutes the statistical signature of different kinds of selection on SSD and should be avoided in future studies.
Evolution, 2009
The origin of sexual size dimorphisms (SSD) has long been a central topic in evolutionary biology. However, there is little agreement as to which factors are most important in driving the evolution of SSD, and several hypotheses concerning SSD evolution have never been tested empirically. Emydid turtles include species with both male and female-biased SSD, and some emydids exhibit among the most extreme SSD in tetrapods. Here, we use a comparative phylogenetic approach in emydids to analyze the origins of SSD and test several hypotheses for the evolution of SSD, some for the first time. We test the Fairbairn-Preziosi hypothesis for the origin of Rensch's rule, and support it in lineages with male-biased SSD but not those with female-biased SSD. We also find support for the secondary ecological dimorphism hypothesis, which proposes that selection for ecological divergence between sexes exaggerates preexisting SSD. Finally, we find only equivocal support for the Bolnick-Doebeli hypothesis, which relates intersexual ecological divergence to interspecific ecological divergence. Our results also illustrate how global analyses of SSD may mislead in groups in which the factors that drive the evolution of SSD vary among clades.
Ecology and Evolution
Turtles have been prominent subjects of sexual size dimorphism (SSD) analyses due to their compact taxonomy, mating systems, and habitat diversity. In prior studies, marine turtles were grouped with fully aquatic non‐marine turtles (NMATs). This is interesting because it is well‐established that the marine environment imposes a distinct selective milieu on body form of vagile vertebrates, driven by convergent adaptations for energy‐efficient propulsion and drag reduction. We generated a comprehensive database of adult marine turtle body sizes (38,569 observations across all species), which we then used to evaluate the magnitude of SSD in marine turtles and how it compares to SSD in NMAT. We find that marine turtles are only minimally sexually size dimorphic, whereas NMAT typically exhibit female‐biased SSD. We argue that the reason for this difference is the sustained long‐distance swimming that characterizes marine turtle ecology, which entails significant energetic costs incurred ...