Demography, sex ratio, and sexual size dimorphism in a northern population of common musk turtles (Sternotherus odoratus)

1996 ◽  
Vol 74 (5) ◽  
pp. 918-925 ◽  
Author(s):  
Jonathan H. Edmonds ◽  
Ronald J. Brooks
Keyword(s):  
Sex Ratio ◽  
Sexual Size Dimorphism ◽  
Differential Mortality ◽  
Adult Males ◽  
Differential Growth ◽  
Size Dimorphism ◽  
Georgian Bay ◽  
Differential Movement ◽  
Sternotherus Odoratus ◽  
Biased Sex Ratio

A population of common musk turtles (Sternotherus odoratus) was studied in Georgian Bay, Ontario, near the northern limit of the species' range, during the summers of 1991–1994. A total of 314 (229 adult males, 68 adult females, and 17 juveniles) turtles were captured, marked, measured, and released. Over the geographic range of S. odoratus there was a positive relationship between body size and latitude, the musk turtles of the Georgian Bay population being significantly larger than those in any of the more southerly populations. The sex ratio was significantly male-biased, and the study population was unique in having sexual size dimorphism, with significantly larger males. We have hypothesized that this dimorphism has arisen through sexual selection that is being driven by the male-biased sex ratio. Male–male competition for mates is intensified and thereby selects for larger males. Proximately, biased sex ratios and sexual size dimorphism in turtles have been attributed to differential ages and sizes at sexual maturity. However, we found no support for this hypothesis in our population. We have attributed sexual size dimorphism to either differential growth rates after maturity or differential mortality of adults. The male-biased sex ratio may be due to differential movement patterns, differential mortality of the sexes, or the effects of ambient temperature on sex determination.

Proximate mechanisms that contribute to female-biased sexual size dimorphism in an anguid lizard

2004 ◽  
Vol 82 (5) ◽  
pp. 817-822 ◽  
Author(s):  
Pamela L Rutherford
Keyword(s):  
Sexual Size Dimorphism ◽  
Growth Parameters ◽  
Large Body ◽  
Growth Curves ◽  
Differential Mortality ◽  
Differential Growth ◽  
Size Dimorphism ◽  
Proximate Mechanisms ◽  
Males And Females ◽  
Standard Life

Various proximate mechanisms have been proposed to explain sexual size dimorphism (SSD) in vertebrates. Identifying the proximate causation of SSD allows insight into the ultimate reasons why SSD exists. I explored whether differential growth rates and (or) mortality explain SSD in the lizard Elgaria coerulea (Baird and Girard, 1852). I estimated growth parameters for males and females using the logistic-by-weight growth curves and determined survivorship using two complimentary methods: standard life-table calculations and capture–recapture methods. The former calculated age-specific survivorship, whereas the latter tested for differences in survivorship between males and females while considering differences in their recapture rates. I considered age-specific SSD as further evidence of SSD independent of differential mortality. Differences in growth asymptote, not intrinsic growth rate, contribute to SSD in this population. SSD is not due to differential mortality, as there is no difference in survivorship of males and females over 3 years of age. In addition, there is age-specific SSD with females larger than males for individuals 4 years of age and greater. The female-biased SSD may be a result of selection for large body size, although further studies are necessary to identify the ultimate cause of SSD in this species.

scholarly journals Evolution of sexual size dimorphism and its relationship with sex ratio in carabid beetles of Genus Ceroglossus Solier

2013 ◽  
Vol 59 (6) ◽  
pp. 769-777 ◽  
Author(s):  
Hugo A. Benítez ◽  
Jorge Avaria-Llautureo ◽  
Cristian B. Canales-Aguirre ◽  
Viviane Jerez ◽  
Luis E. Parra ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sexual Size Dimorphism ◽  
Phylogenetic Signal ◽  
Comparative Method ◽  
Carabid Beetles ◽  
Entire Group ◽  
Geometrical Shape ◽  
Specific Level ◽  
Size Dimorphism ◽  
Morphological Studies

Abstract Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for intense male competition for mates and yet exhibit little or no sexual size dimorphism (SSD). This fact suggest that species with low SSD should be express the effect of evolutionary pressure in non-obvious geometrical shape promoted by sex ratio in an evolutionary time scale. To evaluate this hypothesis we used phylogenetic comparative method in a Bayesian framework to investigate the evolution of SSD and the role of sex ratio at inter-specific level in the species of Ceroglossus (Coleoptera: Carabidae). In our results the proportion farthest from 1:1 is associated with more disparate body shape, even though the entire group has minimum variation in sex ratio, which is an intrinsic life history character of this group considering its phylogenetic conservatism or phylogenetic signal. We suggest that the sex ratio has determined the dimorphism degree during evolution of this group, since both traits have increased or decreased together during the species divergence (i.e. positive phylogenetic correlation: r2≈0.85). We suggest that morphological studies of SSD will benefit from using comparative method with Bayesian approaches to assess the effect of phylogenetic history and its uncertainty. Finally, this will be allow to researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed sexual dimorphism patterns.

scholarly journals Sex Ratio of Small Hive Beetles: The Role of Pupation and Adult Longevity

Insects ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 133 ◽  
Author(s):  
Anna Papach ◽  
Jérémy Gonthier ◽  
Geoffrey R. Williams ◽  
Peter Neumann
Keyword(s):  
Sex Ratio ◽  
Field Studies ◽  
Differential Mortality ◽  
Adult Longevity ◽  
Published Data ◽  
Larval Feeding ◽  
Intraspecific Interactions ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Small Hive Beetles

The sex ratio of sexually reproducing animal species tends to be 1:1, which is known as Fisher’s principle. However, differential mortality and intraspecific competition during pupation can result in a biased adult sex ratio in insects. The female-biased sex ratio of small hive beetles (SHBs) is known from both laboratory and field studies, but the underlying reasons are not well understood. Here, we used laboratory mass and individual pupation to test if differential mortality between sexes and/or intraspecific interactions can explain this sex ratio. The data show a significant female-biased adult sex ratio in both mass and individual rearing, even when assuming that all dead individuals were males. Our results therefore suggest that neither differential mortality during pupation nor intraspecific interactions are likely to explain the female-biased sex ratio of freshly emerged adult SHBs. We regard it as more likely that either competition during the larval feeding stage or genetic mechanisms are involved. In addition, we compared our data with previously published data on the sex ratio of both freshly emerged and field-collected SHBs to investigate possible gender differences in adult longevity. The data show a significantly greater female bias in the sex ratio upon emergence, compared to field-collected SHBs, suggesting that adult females have a shorter longevity.

Male–male contests for mates, sexual size dimorphism, and sex ratio in a natural population of a solitary parasitoid

2013 ◽  
Vol 100 ◽  
pp. 1-8 ◽  
Author(s):  
Margarete V. Macedo ◽  
Ricardo F. Monteiro ◽  
Mariana P. Silveira ◽  
Peter J. Mayhew
Keyword(s):  
Sex Ratio ◽  
Natural Population ◽  
Sexual Size Dimorphism ◽  
Size Dimorphism ◽  
Solitary Parasitoid ◽  
Male Contests

Offspring growth and parental care in sexually dimorphic Nazca boobies (Sula granti)

2007 ◽  
Vol 85 (6) ◽  
pp. 686-694 ◽  
Author(s):  
H.M. Townsend ◽  
T.J. Maness ◽  
D.J. Anderson
Keyword(s):  
Sexual Size Dimorphism ◽  
Poor Performance ◽  
Sexually Dimorphic ◽  
Adult Males ◽  
Parental Effort ◽  
Size Dimorphism ◽  
Sula Granti ◽  
More Care ◽  
Mean Size ◽  
Specific Food

A review of studies on nestling bird food requirements indicates that degree of sexual size dimorphism reliably predicts disparity in sex-specific food requirements, but that parents often fail to meet the excess requirement of the larger sex. We studied a population of Nazca boobies ( Sula granti Rothschild, 1902), a sexually dimorphic pelagic seabird, to determine whether parents provide more care to daughters, the larger sex. Daughters grew to a larger size than did sons during the nestling period, but did not reach the mean size of adult females, while sons exceeded the size of adult males. Estimates of parental effort exerted for sons versus daughters indicated similar levels of effort, and that females fledged in poorer condition than males did in the study year, one of intermediate breeding conditions. Results from another study conducted during better breeding conditions indicated little limitation on growth of either sex. Together, these studies are consistent with a ceiling on parental effort in a long-lived species that allows consistent self-maintenance for parents, but causes poor performance in the costlier sex under poor breeding conditions. Complementary studies of short-lived species are needed to evaluate our suggested linkage between parental effort, self-maintenance, and sexual size dimorphism.

Sexual size dimorphism and food requirements of nestling birds

1993 ◽  
Vol 71 (12) ◽  
pp. 2541-2545 ◽  
Author(s):  
David J. Anderson ◽  
Jo Reeve ◽  
Juan E. Martinez Gomez ◽  
Wesley W. Weathers ◽  
Siobhan Hutson ◽  
...  
Keyword(s):  
Gender Difference ◽  
Sex Ratio ◽  
Sex Allocation ◽  
Sexual Size Dimorphism ◽  
Positive Association ◽  
Size Dimorphism ◽  
American Kestrels ◽  
Sex Allocation Theory ◽  
Strong Positive Association ◽  
And Gender

The food requirements of dependent sons and daughters have important implications for evolution of the sex ratio, according to current sex allocation theory. We studied food requirements of nestling American kestrels (Falco sparverius), a moderately size-dimorphic falcon, by hand-feeding 61 birds from hatching to fledging. Daughters, the larger gender, consumed 6.99% more food than did sons. Sons did not have higher energy expenditure from higher effort during sibling competition than daughters did, so parents must supply more food to satisfy daughters' needs than to satisfy sons'. A review of all related studies shows a strong positive association between the degree of sexual size dimorphism and gender difference in food requirements.

Growth and sexual size dimorphism in Alberta populations of the eastern short-horned lizard, Phrynosoma douglassi brevirostre

1985 ◽  
Vol 63 (1) ◽  
pp. 139-154 ◽  
Author(s):  
G. Lawrence Powell ◽  
Anthony P. Russell
Keyword(s):  
Growth Model ◽  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Growth Models ◽  
Tail Length ◽  
Growth Patterns ◽  
Head Width ◽  
Adult Size ◽  
Adult Males ◽  
Size Dimorphism

Alberta populations of Phrynosoma douglassi brevirostre display marked sexual size dimorphism, adult females being considerably larger than adult males. Discriminant analyses of whole mensural characters and of scaled mensural characters indicate that this dimorphism is present from birth, although it is more strongly expressed after sexual maturity. Recapture data were used to generate modified logistic by weight growth models for snout–vent length (SVL), and allometric models for each sex were generated for growth in tail length, head length, and head width. The SVL growth model for females indicates delayed maturity leading to greater adult size, an expected feature of a female viviparine. The SVL growth model for males indicates that growth ceases sooner than in females, resulting in a smaller adult size. This is possibly a result of male dispersal competition, an hypothesis further borne out by the results of a preliminary analysis of mobility in the two sexes, and may also be influenced by intersexual dietary competition. Differences in head dimensions between the sexes are a function of the differences in SVL at adulthood, but there is a significant sexual difference in the allometric relationship of tail length to SVL. No difference in the growth patterns and adult size of either sex was found to exist over the range in Alberta.

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