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.

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 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.

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.

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.

Egg size, prey size, and sexual size dimorphism in digger wasps (Hymenoptera: Sphecidae)

1985 ◽  
Vol 63 (9) ◽  
pp. 2187-2193 ◽  
Author(s):  
Kevin M. O'Neill
Keyword(s):  
Body Size ◽  
Selection Pressure ◽  
Sexual Size Dimorphism ◽  
Species Selection ◽  
Male Size ◽  
Size Dimorphism ◽  
Female Body Size ◽  
Mean Size ◽  
Males And Females ◽  
Apparent Association

Female digger wasps invest substantially in each of their offspring, laying relatively few, large eggs and providing the young with the insect prey on which they depend for food. In a study of six species in the genera Philanthus, Bembecinus, and Bembix, it was found that within each species, there is a positive correlation between female body size and both the size of their ovarial eggs and the size of the prey they provision. In five of the six species, females were larger than males on average. It is suggested that the apparent association between body size and certain aspects of parental investment by females may provide the directional selection pressure that results in the evolution of sexual size dimorphism in digger wasps. In one species, males and females have the same mean size, probably because, in this species, selection pressure on male size is similar to that on females.

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.

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.

Pattern of sexual size dimorphism supports the inverse of Rensch’s rule in two frog species

2014 ◽  
Vol 64 (1) ◽  
pp. 87-95 ◽  
Author(s):  
Di Lu ◽  
Cai Quan Zhou ◽  
Lian Jun Zhao ◽  
Wen Bo Liao
Keyword(s):  
Body Size ◽  
Sexual Size Dimorphism ◽  
Rana Temporaria ◽  
Rensch’S Rule ◽  
Size Dimorphism ◽  
Rensch's Rule ◽  
Frog Species ◽  
Mean Size ◽  
The Common ◽  
Males And Females

Rensch’s rule describes that sexual size dimorphism (SSD) increases with body size (hyperallometry) when males are larger, and decreases with body size (hypoallometry) when males are smaller. In this paper, on the basis of mean adult body size resulting from 18 populations of the common frogRana temporariaand 24 populations of the Tibetan frogNanorana parkeri, we tested the consistency of allometric relationships between males and females with Rensch’s rule. Our results show that the variation in degree of female-biased SSD increased with increasing mean size at intraspecific levels in two species, which is consistent with the inverse of Rensch’s rule. Furthermore, we tested the hypothesis that the degree of SSD decreased with increasing altitudes. Inconsistent with the predications of our hypothesis, we found no relationships between the degree of SSD and altitude for the two species investigated. These findings suggest that females living in adverse climates in high altitudes cannot adjust their body size as plastically as males.

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.

Differences in Sexual Size Dimorphism and Body Proportions between Adult and Subadult House Sparrows in North America

The Auk ◽  
1987 ◽  
Vol 104 (4) ◽  
pp. 681-687 ◽  
Author(s):  
W. Bruce McGillivray ◽  
Richard F. Johnston
Keyword(s):  
Body Size ◽  
Sexual Size Dimorphism ◽  
House Sparrow ◽  
Passer Domesticus ◽  
Adult Males ◽  
House Sparrows ◽  
Size Dimorphism ◽  
Winter Temperatures ◽  
Body Core ◽  
Strong Body

Abstract North American samples of House Sparrows (Passer domesticus) collected by R. F. Johnston and R. K. Selander (see Johnston and Selander 1971, Johnston 1973) were separated into adult (19 localities) and subadult (21 localities) groups. Significant clines were generated for all age and sex combinations through regression of locality means for body size against environmental seasonality. The strong body-size clines for subadult House Sparrows suggest a large genetic component to geographic variation in House Sparrow body size. There were no significant differences between the male and female clines for either age group. Therefore, there was no consistent relationship between sexual size dimorphism (SSD) in adult House Sparrow populations and environmental factors. Adult levels of SSD were higher than subadult levels at localities with distinct seasonalities. This resulted from selection against relatively large subadult females in areas with cold winters. Adult males were larger than subadult males, but whether this represented growth or selection is equivocal. The ratio of body core to limb variables was correlated poorly with the winter temperatures of the collecting localities. The relationship improved if samples from coastal areas were excluded. Adult levels of this ratio were higher than subadult levels at localities with low January temperatures. Overwinter changes in both House Sparrow size and shape can be correlated with environmental variables. Although selection for efficient thermoregulatory design is implied, it is difficult to account for the mortality of large subadult females over cold winters and to completely discount the effects of growth.

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