On the male of the orb weaving spider Micrathena cyanospina (Lucas, 1835) (Araneidae, Araneae)

Zootaxa ◽  
2011 ◽  
Vol 3096 (1) ◽  
pp. 64
Author(s):  
ANDRÉ A. NOGUEIRA ◽  
ANTONIO D. BRESCOVIT
Keyword(s):  
Adult Female ◽  
Sexual Size Dimorphism ◽  
Female Size ◽  
Sexually Dimorphic ◽  
Adult Males ◽  
Size Dimorphism ◽  
Female Gigantism

Most species of spiders exhibit some degree sexual size dimorphism (SSD). Females are usually larger than males, about 20% on average (Vollrath 1998), although this difference can be much larger. By convention, species in which the adult males are half or less of the adult female size are considered sexually dimorphic, some representing cases of extreme SSD (Hormiga et al. 2000). It is worth mentioning that although males are called dwarfs, large SSD is often a consequence of female gigantism rather than male dwarfism (Hormiga et al. 2000).

Sexual size dimorphism in the viviparous caecilian amphibian Geotrypetes seraphini seraphini (Gymnophiona: Dermophiidae) including an updated overview of sexual dimorphism in caecilian amphibians

2016 ◽  
Vol 37 (3) ◽  
pp. 291-299 ◽  
Author(s):  
Markus Maerker ◽  
Sandy Reinhard ◽  
Peter Pogoda ◽  
Alexander Kupfer
Keyword(s):  
Sexual Dimorphism ◽  
Body Length ◽  
Sexual Size Dimorphism ◽  
Molecular Ecology ◽  
Female Size ◽  
Sexually Dimorphic ◽  
Size Dimorphism ◽  
Mating System Evolution ◽  
Accurate Comparison ◽  
Widespread Phenomenon

Sexual size dimorphism (SSD) describing intersexual size differences of a given taxon is a widespread phenomenon in the animal kingdom. SSD plays a significant role in understanding life history and mating system evolution. The snakelike morphology of limbless caecilian amphibians lacking obvious secondary sexual characters (in contrast to frogs and salamanders) impedes an accurate comparison between sexes.Here, the phylogenetically derived teresomatan and viviparous caecilianGeotrypetes seraphini seraphiniwas analysed for patterns of sexual dimorphism. In terms of body size females were the larger sex, but when body length was adjusted male-biased intersexual differences in cloacal shape appeared. The larger female size is likely explained by fecundity selection as clutch size was positively correlated to female body length. Unexpectedly a cryptic, ontogeny related variation of the nuchal collars was found. An overview of SSD in caecilians including data for 27 species of nine out of ten existing families revealed a quite high number of taxa showing sexually dimorphic head size dimensions exclusively present among phylogenetically derived teresomatan caecilians. Still further research including insights into the behavioural ecology and molecular ecology of mating systems is warranted to better understand the evolution of sexual size dimorphism of caecilian amphibians.

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 geographic variation in forearm length of Rafinesque’s Big-eared Bat (Corynorhinus rafinesquii) and Southeastern Myotis (Myotis austroriparius)

Mammalia ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jessica M. Vannatta ◽  
Brian D. Carver
Keyword(s):  
Regional Variation ◽  
Sexual Size Dimorphism ◽  
Sexually Dimorphic ◽  
Size Dimorphism ◽  
Corynorhinus Rafinesquii ◽  
Southeastern Myotis ◽  
Morphological Measurement ◽  
Sexual Recognition ◽  
Myotis Austroriparius ◽  
Forearm Length

Abstract Sexual size dimorphism is common in many taxa and results from various pressures, including competition, reproductive requirements, functional differences, and sexual recognition. For mammals, males are typically the larger sex; however, for vespertilionid bats, females are more often the larger sex. Forearm length, a feature that influences overall wing and body size and is often sexually dimorphic, is a standard morphological measurement taken from bats. Forearm length was measured in two vesper bat species (Corynorhinus rafinesquii and Myotis austroriparius) that co-occur across much of the southeastern United States. Forearm length was greater in females of both species, and females of both species also exhibited regional variation in forearm length. By having a longer forearm and therefore being larger in size, females may be more maneuverable and better equipped to carry young. While this study did not directly investigate the mechanisms behind regional variation in forearm length, it is possible this is the result of variability in habitat types, resources, or thermodynamic constraints. Knowledge of sexually dimorphic characteristics is important for obtaining a general understanding of a species and its morphology.

Sexual Size Dimorphism and Survival of Male and Female Blackbirds (Icteridae)

The Auk ◽  
1981 ◽  
Vol 98 (3) ◽  
pp. 457-465 ◽  
Author(s):  
William A. Searcy ◽  
Ken Yasukawa
Keyword(s):  
Sexual Size Dimorphism ◽  
Relative Survival ◽  
Female Size ◽  
Male Size ◽  
Size Dimorphism ◽  
Large Size ◽  
Survival Selection ◽  
Female Survival ◽  
Positive Correlations ◽  
Dimorphic Species

Abstract In a between-species comparison of icterids, male survival decreases relative to female survival as the degree of sexual size dimorphism increases. This result is consistent with the hypothesis that male size is limited by survival selection in icterids; the degree of size dimorphism is known to correlate with the degree of polygyny in icterids, however, so the decreased relative survival of males in dimorphic species may be caused by some correlate of polygyny other than large size. Survival estimates based on records of recovery of dead birds show positive correlations between male size and male survival and between female size and female survival, but survival estimates based on recaptures of live birds fail to show such relationships.

Spatial variability in the social organisation of the yellow-bellied glider (Petaurus australis) near Ravenshoe, north Queensland

2001 ◽  
Vol 49 (4) ◽  
pp. 397 ◽  
Author(s):  
Ross L. Goldingay ◽  
Darren G. Quin ◽  
Sue Churchill
Keyword(s):  
Adult Female ◽  
Social System ◽  
Dominant Male ◽  
Female Group ◽  
Sexually Dimorphic ◽  
Adult Males ◽  
Adult Females ◽  
The Social ◽  
Natal Home ◽  
Petaurus Australis

A detailed study was conducted over a 12-month period of 10 yellow-bellied glider groups at Nitchaga Creek in north Queensland. Adult gliders were sexually dimorphic in body size and were characterised by yellow ventral fur, which is consistent with southern populations. Gliders lived in groups of 3–6 individuals that occupied exclusive areas of about 50 ha. The structure of glider groups varied enormously: five contained one adult pair, three contained one adult male and 2–3 adult females, and two initially contained 2–3 adult males and one adult female but then persisted as bachelor groups after the death or disappearance of the adult female. Group size changed during the year as offspring matured and as individuals died. One male glider dispersed about 1 km from its natal home-range and became the dominant male in a nearby group. Young were born throughout the year, with a peak in the number of pouch-young in June. This study has confirmed the highly variable social system of the yellow-bellied glider, which appears to be mediated by local resource abundance.

Geographic variation in body size and sexual size dimorphism of North American Ratsnakes (Pantherophis spp. s.l.)

2018 ◽  
Vol 96 (11) ◽  
pp. 1196-1202 ◽  
Author(s):  
Brett A. DeGregorio ◽  
Gabriel Blouin-Demers ◽  
Gerardo L.F. Carfagno ◽  
J. Whitfield Gibbons ◽  
Stephen J. Mullin ◽  
...  
Keyword(s):  
Body Size ◽  
Large Scale ◽  
Sexual Size Dimorphism ◽  
Size Variation ◽  
Sexually Dimorphic ◽  
Male Body ◽  
Complex Species ◽  
Size Dimorphism ◽  
Body Size Variation ◽  
Female Body Size

Because body size affects nearly all facets of an organism’s life history, ecologists have long been interested in large-scale patterns of body-size variation, as well as why those large-scale patterns often differ between sexes. We explored body-size variation across the range of the sexually dimorphic Ratsnake complex (species of the genus Pantherophis Fitzinger, 1843 s.l.; formerly Elaphe obsoleta (Say in James, 1823)) in North America. We specifically explored whether variation in body size followed latitudinal patterns or varied with climatic variables. We found that body size did not conform to a climatic or latitudinal gradient, but instead, some of the populations with the largest snakes occurred near the core of the geographic range and some with the smallest occurred near the northern, western, and southern peripheries of the range. Males averaged 14% larger than females, although the degree of sexual size dimorphism varied between populations (range: 2%–25%). There was a weak trend for male body size to change in relation to temperature, whereas female body size did not. Our results indicate that relationships between climate and an ectotherm’s body size are more complicated than linear latitudinal clines and likely differ for males and females.

Egg-laying site, fecundity and degree of sexual size dimorphism in frogs

2020 ◽  
Vol 131 (3) ◽  
pp. 600-610
Author(s):  
Nelson Rodrigues Silva ◽  
Bianca V M Berneck ◽  
Helio R da Silva ◽  
Célio F B Haddad ◽  
Kelly R Zamudio ◽  
...  
Keyword(s):  
Sexual Size Dimorphism ◽  
Egg Laying ◽  
Female Size ◽  
Selective Force ◽  
Size Dimorphism ◽  
Body Sizes ◽  
Space Limitation ◽  
Males And Females ◽  
Similar Body ◽  
Oviposition Sites

Abstract Female fecundity is an important selective force leading to female-biased sexual size dimorphism (SSD) in frogs. Because anurans exhibit diverse reproductive modes, we investigated whether variation in SSD and fecundity are related with oviposition site. We asked whether arboreal breeding species show pronounced female-biased SSD and if, paradoxically, females have lower fecundity because of the costs of carrying oocytes and amplectant males. Conversely, we tested whether species that deposit eggs in concealed sites show less pronounced SSD, because females do not carry males and space limitation may reduce female size and fecundity. Our results showed that, in general, males were approximately 20% smaller than females. However, for species with hidden oviposition sites, males and females exhibited more similar body sizes and arboreal hylids showed more pronounced female-biased SSD. Overall, fecundity was higher in aquatic breeders, as expected, but in hylids, fecundity was smaller in arboreal breeders, which suggests that arboreality may impose restrictions on fecundity. By analysing SSD in a broader and more specific lineage (Hylidae), we found that reproductive microhabitat may also influence female size and fecundity, playing an important role in the evolution of SSD in frogs at different evolutionary scales.

Male and female pups of the highly sexually dimorphic northern elephant seal (Mirounga angustirostris) differ slightly in body size

2019 ◽  
Vol 97 (3) ◽  
pp. 241-250
Author(s):  
E. Salogni ◽  
F. Galimberti ◽  
S. Sanvito ◽  
E.H. Miller
Keyword(s):  
Body Size ◽  
Early Life ◽  
Sexual Size Dimorphism ◽  
Elephant Seal ◽  
Sexually Dimorphic ◽  
Mirounga Angustirostris ◽  
Northern Elephant Seal ◽  
Size Dimorphism ◽  
Selective Forces ◽  
Size At Birth

In mammals, males generally are larger than females, though such sexual-size differences have been documented primarily in adults and are relatively poorly known in early life. We studied sexual-size differences in pups of the northern elephant seal (Mirounga angustirostris (Gill, 1866)), which in adulthood is one of the most sexually dimorphic mammals. We studied body size at birth and weaning, at Islas San Benito, Mexico, at the southernmost limit of the species’ breeding range. Males were 10% heavier and 2% longer than females at birth. Sexes did not differ significantly in either measure of body size at weaning, although males were slightly heavier (4%) and longer (1%) than females. Neither growth rate nor suckling duration differed between the sexes. In previous studies in California, USA, pups at weaning were heavier than in our study, and males were heavier than females. These differences may reflect ecological, temporal, or life-history differences across populations. The modest difference in sexual-size dimorphism early in life in this species compared with the great difference in adulthood likely reflects multiple selective forces, including constraints on neonatal size set by body size of females, and the weakness of sexual selection at that stage of life.

Reproduction of Psammodromus algirus in coastal sandy areas of NE Spain

1997 ◽  
Vol 18 (4) ◽  
pp. 369-382 ◽  
Author(s):  
Miguel A. Carretero ◽  
Gustavo A. Llorente
Keyword(s):  
Ecological Niche ◽  
Sexual Size Dimorphism ◽  
Reproductive Traits ◽  
Reproductive Season ◽  
Breeding Period ◽  
Female Size ◽  
Size Dimorphism ◽  
Common Trend ◽  
Psammodromus Algirus ◽  
Ne Spain

AbstractThe variation in the reproductive cycle of three populations of the lizard Psammodromus algirus living in coastal sandy areas of NE Spain was analyzed. In contrast with those in continental climates, they showed evidence of reproductive stress: the reproductive season began sooner and was longer. Moreover, body size was smaller and sexual size dimorphism did not arise. Only the end of the breeding period was relatively constant. Nevertheless, these different reproductive traits seem to follow a common trend. In general, no important reproductive differences were found among the three coastal areas. Females laying two clutches have been detected in one locality. Clutch size was correlated with female size. The high phenological plasticity of this species is associated with its wide ecological niche.

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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