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166 results for “sexual size dimorphism”
Data from: How sexual and natural selection shape sexual size dimorphism: evidence from multiple evolutionary scales
1. Sexual size dimorphism (SSD) is pervasive across taxa and reflects differences in the effects of sexual and natural selection on body size between the sexes. However, disentangling the complex eco-evolutionary interactions between these two mechanisms remains a major challenge for biologists. 2. Here, we combine macro-evolutionary (between-species), local evolutionary (between-population) and fine-scale evolutionary (within-population) patterns of SSD to explore how sexual and natural selection interact and shape the evolution of SSD in Australian agamid lizards. Australian agamid lizards show substantial variation in SSD, ecological traits and species density making them an ideal study system to address this question. 3. At the between-species level, population density, ecological generalism and mean species size significantly predict SSD variation, however, only ecological generalism was found to significantly explain variation in larger than average male-biased SSD. At the population level, density positively correlated with SSD in native habitats, but not city park habitats. Last, agonistic behaviour acted as the primary driver of SSD at the within-population level. 4. Our results indicate how sexual and natural selection can interact at different evolutionary scales, and show the importance of considering both selective mechanisms when investigating patterns of SSD.
Data from: Macroecological patterns of sexual size dimorphism in turtles of the world
Sexual size dimorphism (SSD) is a well-documented phenomenon in both plants and animals; however, the ecological and evolutionary mechanisms that drive and maintain SSD patterns across geographic space at regional and global scales are understudied, especially for reptiles. Our goal was to examine geographic variation of turtle SSD and to explore ecological and environmental correlates using phylogenetic comparative methods. We use published body size data on 135 species from nine turtle families to examine how geographic patterns and the evolution of SSD are influenced by habitat specialization, climate (annual mean temperature and annual precipitation) and climate variability, latitude, or a combination of these predictor variables. We also found that geographic variation, magnitude, and direction of turtle SSD are best explained by habitat association, annual temperature variance, and annual precipitation. Use of semi-aquatic and terrestrial habitats was associated with male-biased SSD, whereas use of aquatic habitat was associated with female-biased SSD. Our results also suggest that greater temperature variability is associated with female-biased SSD. In contrast, wetter climates are associated with male-biased SSD compared with arid climates that are associated with female-biased SSD. We also show support for a global latitudinal trend in SSD, with females being larger than males towards the poles, especially in the families Emydidae and Geoemydidae. Estimates of phylogenetic signal for both SSD and habitat type indicate that closely related species occupy similar habitats and exhibit similar direction and magnitude of SSD. These global patterns of SSD may arise from sex-specific reproductive behavior, fecundity, and sex-specific responses to environmental factors that differ among habitats and vary systematically across latitude. Thus, this study adds to our current understanding that while SSD can vary dramatically across and within turtle species under phylogenetic constraints, it may be driven, maintained, and exaggerated by habitat type, climate, and geographic location.
Data from: The causal relationship between sexual selection and sexual size dimorphism in marine gastropods
Sexual size dimorphism is widespread among dioecious species but its underlying driving forces are often complex. A review of sexual size dimorphism in marine gastropods revealed two common patterns: firstly, sexual size dimorphism, with females being larger than males, and secondly females being larger than males in mating pairs; both of which suggest sexual selection as being causally related with sexual size dimorphism. To test this hypothesis, we initially investigated mechanisms driving sexual selection on size in three congeneric marine gastropods with different degrees of sexual size dimorphism, and, secondly, the correlation between male/female sexual selection and sexual size dimorphism across several marine gastropod species. Male mate choice via mucus trail following (as evidence of sexual selection) was found during the mating process in all three congeneric species, despite the fact that not all species showed sexual size dimorphism. There was also a significant and strong negative correlation between female sexual selection and sexual size dimorphism across 16 cases from seven marine gastropod species. These results suggest that sexual selection does not drive sexual size dimorphism. There was, however, evidence of males utilizing a similar mechanism to choose mates (i.e. selecting a female slightly larger than own size) which may be widespread among gastropods, and in tandem with present variability in sexual size dimorphism among species, provide a plausible explanation of the observed mating patterns in marine gastropods.
Data from: Leaf size in three generations of a dioecious tropical tree, Ocotea tenera (Lauraceae): sexual dimorphism and changes with age
PREMISE OF THE STUDY: In dioecious species, selection should favor different leaf sizes in males and females whenever the sexes experience distinct environments or constraints, such as different costs of reproduction. We took advantage of a long-term experimental study of Ocotea tenera (Lauraceae), a dioecious understory tree in Monteverde, Costa Rica, to explore leaf size differences between genders and age classes across generations. METHODS: We measured leaf size in adult trees in a natural population, in their adult F1 offspring in two experimental populations, and in their F2 offspring at the seedling stage. Individual trees were measured at various times over a 20-year period. RESULTS: Leaves of female trees averaged 8% longer and 12% greater in area than those of males. Leaves were sexually dimorphic at reproductive maturity. Leaf size declined over the course of most trees' lifetimes. Heritability estimates for leaf length were positive although not statistically significant (h2 = 0.63, SE = 0.48, P= 0.095). CONCLUSIONS: We ruled out the "ecological causation" hypothesis for sexual dimorphism in leaf size because male and female trees co-occurred in the same habitats. Sexual dimorphism appeared not to result from genetic or phenotypic correlations with other traits such as height or flower size. Rather, females appear to compensate for higher costs of reproduction and diminished photosynthetic capacity by producing larger leaves. Additive genetic variance in leaf size, a prerequisite for an evolutionary response to selection for sexual dimorphism, was suggested by positive (although only marginally significant) heritability estimates.
Data from: Sneaker males affect fighter male body size and sexual size dimorphism in salmon
Large male body size is typically favored by directional sexual selection through competition for mates. However, alternative male life-history phenotypes, such as "sneakers," should decrease the strength of sexual selection acting on body size of large "fighter" males. We tested this prediction with salmon species; in southern populations, where sneakers are common, fighter males should be smaller than in northern populations, where sneakers are rare, leading to geographical clines in sexual size dimorphism (SSD). Consistent with our prediction, fighter male body size and SSD (fighter male∶female size) increase with latitude in species with sneaker males (Atlantic salmon Salmo salar and masu salmon Oncorhynchus masou) but not in species without sneakers (chum salmon Oncorhynchus keta and pink salmon Oncorhynchus gorbuscha). This is the first evidence that sneaker males affect SSD across populations and species, and it suggests that alternative male mating strategies may shape the evolution of body size.
FIGURES 1 – 12 in A new species of Ferorhinella with an unusual pattern of sexual size dimorphism (Hemiptera, Cercopidae, Tomaspidinae)
FIGURES 1 – 12. Ferorhinella balatra sp. nov. 1. Holotype male, dorsal view. 2. Paratype female, dorsal view. 3. Holotype male, lateral view. 4. Paratype female, lateral view. 5. Subgenital plate, lateral view. 6. Paramere, external view. 7. Aedeagus, lateral view. 8. Aedeagus, dorsal view. 9. Female pygofer and valvulae. 10. First valvulae of ovipositor. 11. Second valvulae of ovipositor.
Fig. 2 in Sexual Size and Shape Dimorphism in Dineutus nigrior (Coleoptera: Gyrinidae)
Fig. 2. Relationships between standardized body length and other body size measures in male and female Dineutus nigrior. Filled circles and solid lines indicate males; open circles and broken lines indicate females. Male n 5 63, female n 5 362–363.
Fig. 1 in Sexual Size and Shape Dimorphism in Dineutus nigrior (Coleoptera: Gyrinidae)
Fig. 1. Frequency distribution of canonical discriminant scores for male and female Dineutus nigrior.
Data and code from Wang et al. "An evaluation of sexual dimorphism in head size and shape in Red Salamanders (Pseudotriton ruber)"
<p>Data and code from Wang et al., "An evaluation of sexual dimorphism in head size and shape in Red Salamanders (<em>Pseudotriton ruber</em>)"</p>
An evolutionary explanation of female-biased sexual size dimorphism in North Sea plaice, Pleuronectes platessa L.
<p>Sexual size dimorphism (SSD) is caused by differences in selection pressures and life-history trade-offs faced by males and females. Proximate causes of SSD may involve sex-specific mortality, energy acquisition, and energy expenditure for maintenance, reproductive tissues, and reproductive behavior. Using a quantitative, individual-based, eco-genetic model parameterized for North Sea plaice, we explore the importance of these mechanisms for female-biased SSD, under which males are smaller and reach sexual maturity earlier than females (common among fish, but also arising in arthropods and mammals). We consider two mechanisms potentially serving as ultimate causes: (a) Male investments in male reproductive behavior might evolve to detract energy resources that would otherwise be available for somatic growth, and (b) diminishing returns on male reproductive investments might evolve to reduce energy acquisition. In general, both of these can bring about smaller male body sizes. We report the following findings. First, higher investments in male reproductive behavior alone cannot explain the North Sea plaice SSD. This is because such higher reproductive investments require increased energy acquisition, which would cause a delay in maturation, leading to male-biased SSD contrary to observations. When accounting for the observed differential (lower) male mortality, maturation is postponed even further, leading to even larger males. Second, diminishing returns on male reproductive investments alone can qualitatively account for the North Sea plaice SSD, even though the quantitative match is imperfect. Third, both mechanisms can be reconciled with, and thus provide a mechanistic basis for, the previously advanced Ghiselin–Reiss hypothesis, according to which smaller males will evolve if their reproductive success is dominated by scramble competition for fertilizing females, as males would consequently invest more in reproduction than growth, potentially implying lower survival rates, and thus relaxing male–male competition. Fourth, a good quantitative fit with the North Sea plaice SSD is achieved by combining both mechanisms while accounting for sex-specific costs males incur during their spawning season. Fifth, evolution caused by fishing is likely to have modified the North Sea plaice SSD.</p>
Data from: Structural complexity of hunting habitat and territoriality increase the reversed sexual size dimorphism in diurnal raptors
Despite numerous efforts and many hypotheses to explain the selective pressures that may have favoured reversed sexual dimorphism (RSD) in raptors ‐ i.e. that the female is larger than the male ‐ some drivers of RSD are still unknown. Here we analyse how much variation in RSD is explained by hunting habitat structure, territoriality or territory size. We do so using data on diurnal raptors from the New World and the Western Palearctic – i.e. Cathartidae, Pandionidae, Accipitridae and Falconidae, the largest bird group showing RSD ‐ taking into account the phylogenetic relationships among species. Our results identify the type of the main prey as a major factor explaining RSD in raptors. We also found RSD to increase with increasing structural complexity in the hunting habitat from open or semi‐open habitats to forest interior. RSD also increased with increasing degree of territoriality of the species (non‐territorial < facultative < territorial). Finally, for territorial species RSD increased with increasing size of nesting territory. A model comprising only three predictor variables (prey type, structural complexity of hunting habitat and territoriality) explained up to 50% of the variation in RSD of European and American diurnal raptor species, and up to 40% of the variation in RSD when only territorial species were considered. Our results highlight the relevance of spatial facets of the niche – e.g. hunting habitat, territoriality and territory size ‐ in exerting selective pressures on the body size of diurnal raptors. These selective pressures, joint with already known trophic factors – e.g. diet ‐ are decisive for the evolution of the RSD, a key trait in the functional ecology of raptors. Our findings open up new perspectives in the study of sexual size divergence in birds.
Figure 2 in Geographic variation in body size and sexual size dimorphism in the giant spiny frog Paa spinosa (David, 1875) (Anura: Ranoidae)
Figure 2. The sexual size dimorphism (SSD) ratio of five populations. SSD ratio = mean body size of the male/mean body size of the female.
Figure 1 in Geographic variation in body size and sexual size dimorphism in the giant spiny frog Paa spinosa (David, 1875) (Anura: Ranoidae)
Figure 1. Map of South China showing localities where Paa spinosa was sampled for analyses of geographic variation in body size. Names of sampling localities and geographic coordinates are as follows: JH: JinHua (29°32′ N, 119°33′ E). LS: LiShui (28°27′ N, 119°54′ E). PJ: Pingjiang (28°72′ N, 113°58′ E). JGS: JinGangshan (26°34′ N, 114°10′ E). YS: YangShan (24°48′ N, 112°63′ E).
Figures 33–41 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figures 33–41. Species included in this study. Fig. 33. Micrathena spinosa, female internal genitalia, dorsal, cleared. Fig. 34. Micrathena horrida, female internal genitalia, dorsal, cleared. Fig. 35. Micrathena fissispina, female internal genitalia, dorsal, cleared. Fig. 36. Micrathena schreibersi, female internal genitalia, dorsal, cleared. Fig. 37. Chaetacis aureola, male first tibia, lateral. Fig. 38. Micrathena schreibersi, male palpus, retrolateral. Fig. 39. Micrathena bifida, male palpus, mesal. Fig. 40. Micrathena swainsoni, male palpus, apical. Fig. 41. Micrathena bifida, male palpus, retrolateral. Abbreviations: BP, basal projection of the median apophysis; C, conductor; CL, conductor lobe; CM, conductor basal membrane; Cy, cymbium; DP, digitiform projection of the median apophysis; E, embolus; MA, median apophysis rim; MAL, median apophysis lobe; Me, metatarsus; P, paracymbium; Pa, patella; PH, paracymbium hump; PM, paramedian apophysis; R, radix; S, spermathecae; SP, spermathecae projections; ST, subtegulum; Ta, tarsus; TA, terminal apophysis; TAP, terminal apophysis projection; Ti, tibia; TM, tibial macrosetae; TP, tegular projection. Scale bars = 0.1 mm except 40 = 0.5 mm.
Figures 26–32 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figures 26–32. Species included in this study. Fig. 26. Micrathena furcata, female carapace, dorsal. Fig. 27. Micrathena digitata, female sternum, ventral. Fig. 28. Micrathena spitzi, female sternum, ventral. Fig. 29. Micrathena spinosa, female sternum, ventral. Fig. 30. Micrathena digitata, abdomen end, lateral. Fig. 31. Micrathena lepidoptera, female abdomen, ventral. Fig. 32. Micrathena spinosa, epigynum and booklungs, ventral. Abbreviations: EP, epigynum sclerotized plate; LMA, large median apodeme; LPB, lateral pigmented bands; MPS, median pigmented stripe; PSL, posterior spine lobe; SA, small apodeme; SpA, spinnerets apodeme; SR, spinnerets sclerotized ring; ST, spinnerets tubercle; VS, ventral spines. Scale bars: 26, 29, 30, 31, 32 = 1 mm; 27, 28 = 0.5 mm.
Figures 22–25 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figures 22–25. Scanning electron microscopy images of species included in the current study. Fig. 22. Wagneriana dimastophora, male copulatory bulb, mesal. Fig. 23. Micrathena nigrichelis, female eye region, dorsolateral. Arrow indicates the post-ocular macroseta. Fig. 24. Gasteracantha. cancriformis, female carapace, dorsolateral. Fig. 25. Micrathena plana, female carapace, dorsolateral. Abbreviations: ALE, anterior lateral eye; AME, anterior median eye; BL, bulb length; BW, bulb width; C, conductor; CH, cephalic hump; E, embolus; LSR, lateral setae rows; MA, median apophysis rim; P, pleura; PLE, posterior lateral eye; PM, paramedian apophysis; PME, posterior median eye; R, radix; TA, terminal apophysis; TF, thoracic fovea; TP, tegular projection.
Figures 18–21 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figures 18–21. Scanning electron microscopy images of species included in the current study. Fig. 18. Chaetacis aureola, female fourth leg, ventral. Fig. 19. Micrathena horrida, epigynum, and book lung covers, anterolateral. Circles indicate anterior apodemes. Fig. 20. Micrathena nigrichelis, epigynum, subventral. Fig. 21. Micrathena nigrichelis, male copulatory bulb, mesal. Abbreviations: BP, basal projection of the median apophysis; C, conductor; CL, conductor lobe; CO, copulatory openings; CS, coxal spines; E, embolus; EL, epigynum lobe; FSB, femoral setal bases; LP, epigynum lateral plates; MA, median apophysis rim; PM, paramedian apophysis; R, radix; SF, booklung stridulating files; TA, terminal apophysis; TB, epigynum transverse bar; TP, tegular projection.
Figure 10 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figure 10. Optimization of the lengths of the first (left) and second (right) pairs of posterior spines under a squaredchange parsimony model. Values are expressed as a proportion of carapace length. Darker values indicate greater lengths and the scale is the same for both traits. Spines are considered to be extremely elongated if longer than the carapace. Micrathena spiders are highlighted by the grey background.
Figure 11 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figure 11. Optimization of female (left) and male (right) carapace lengths under a squared-change parsimony model. Values are expressed in millimetres. Darker values indicate greater lengths and the scale is the same for both sexes. The greater the difference of tone between males and females, the higher the sexual size dimorphism for a given species. Micrathena spiders are highlighted by the grey background.
Figure 7 in Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines
Figure 7. Character optimizations of the discrete data set in the tree obtained through implied-weighted parsimony (k = 5). Character numbers are indicated above circles and character states are indicated below circles. Filled circles indicate convergence-free apomorphies, open circles represent homoplasious synapomorphies. For character descriptions, see Appendix 1. The grids near the nodes represent a sensitivity analysis using different values of k; open cells represent presence of the corresponding clade in a given weighting scheme, whereas filled cells represent its absence. Different Micrathena species groups are indicated by the alternating background colour. Scale bar = 2.0 mm. All spiders (females at left, males at right) drawn to scale and printed approximately at natural sizes. Continued in Figs 8 and 9.
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