Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

2014 ◽  
Vol 4 (4) ◽  
pp. 242-247
Author(s):  
ZHAO Wei ◽  
LIU Naifa
Keyword(s):  
Sexual Dimorphism ◽  
Head Size ◽  
Niche Divergence ◽  
Food Niche

Factors driving sexual dimorphism and colour variability in the Achala Copper Lizard (Pristidactylus achalensis), an endemic species to the highland mountains in central Argentina

2020 ◽  
Vol 98 (6) ◽  
pp. 377-389
Author(s):  
S. Naretto ◽  
M. Chiaraviglio
Keyword(s):  
Sex Differences ◽  
Spatial Distribution ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Endemic Species ◽  
Morphological Changes ◽  
Head Size ◽  
Head Width ◽  
Temporal And Spatial Distribution ◽  
Central Argentina

The intensity of mating competition varies according to the temporal and spatial distribution of individuals. Measuring sexual dimorphism over time and interpreting the association between individuals is therefore important if we aim to understand how sexual traits are influenced. We examined sex differences in the Achala Copper Lizard (Pristidactylus achalensis (Gallardo, 1964)), an endemic species from the highest part of mountains of central Argentina. Over 4 years, we explored sex-specific variation in body size, head size, interlimb length, and body colouration. Furthermore, we evaluated how these traits varied temporally, and we also explored whether the spatial distribution of individuals is explained by variation in these traits. We found that P. achalensis is a species with sexual dimorphism in multiple characters, including body size, head size, and colouration. Interestingly, some traits related to mating, such as head width, show a temporal variability in both sexes, whereas other traits, such as colouration, varies seasonally only in males. Our results underline the intriguing possibility of seasonal morphological changes related to mating, and more broadly that sex differences are influenced by sexual selection pressures mediated by temporal variation in mate competition.

Heads or tails? Sexual dimorphism in helodermatid lizards

2007 ◽  
Vol 85 (1) ◽  
pp. 92-98 ◽  
Author(s):  
C.M. Gienger ◽  
Daniel D. Beck
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Morphological Traits ◽  
Tail Length ◽  
Repeated Sequences ◽  
Analysis Of Covariance ◽  
Head Size ◽  
Heloderma Suspectum

We tested the hypothesis that helodermatid lizards (Gila monsters, Heloderma suspectum Cope, 1869, and beaded lizards, H. horridum (Wiegmann, 1829)) show sexual dimorphism in morphological traits related to male–male agonistic behaviors. Male–male combat in helodermatid lizards involves repeated sequences of ritualized grappling. Male Gila monsters use their heads in attempts to gain or maintain a superior position during repeated combat bouts that may last for hours. Pairs of fighting male beaded lizards form spectacular body arches, with abdomens adpressed and snouts, forelimbs, and tail tips contacting the ground. We measured body size, head size, and tail length in 208 preserved H. suspectum, and body size and tail length (but not head size) in 79 live H. horridum, then tested for sexual dimorphism using analysis of covariance. Male Gila monsters had proportionately larger heads than females but did not differ in tail length or body size. Male beaded lizards had proportionately longer tails than females and were larger in body size only when the largest individuals were included in the analysis. Differences in head dimensions (in H. suspectum) and tail length (in H. horridum) are likely the result of sexual selection acting through male–male agonistic behaviors in this unique lizard taxon.

scholarly journals Sexual dimorphism in size and shape of the head in the sea snake Emydocephalus annulatus (Hydrophiinae, Elapidae)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Richard Shine ◽  
Claire Goiran
Keyword(s):  
Sex Differences ◽  
Sexual Dimorphism ◽  
Body Length ◽  
Field Studies ◽  
Head Size ◽  
Head Shape ◽  
Fish Eggs ◽  
Sea Snake ◽  
Size And Shape ◽  
Prey Items

AbstractIn snakes, divergence in head size between the sexes has been interpreted as an adaptation to intersexual niche divergence. By overcoming gape-limitation, a larger head enables snakes of one sex to ingest larger prey items. Under this hypothesis, we do not expect a species that consumes only tiny prey items to exhibit sex differences in relative head size, or to show empirical links between relative head size and fitness-relevant traits such as growth and fecundity. Our field studies on the sea snake Emydocephalus annulatus falsify these predictions. Although these snakes feed exclusively on fish eggs, the heads of female snakes are longer and wider than those of males at the same body length. Individuals with wider heads grew more rapidly, reproduced more often, and produced larger litters. Thus, head shape can affect fitness and can diverge between the sexes even without gape-limitation. Head size and shape may facilitate other aspects of feeding (such as the ability to scrape eggs off coral) and locomotion (hydrodynamics); and a smaller head may advantage the sex that is more mobile, and that obtains its prey in narrow crevices rather than in more exposed situations (i.e., males).

scholarly journals Is sexual size dimorphism in relative head size correlated with intersexual dietary divergence in West African forest cobras, Naja melanoleuca?

2002 ◽  
Vol 71 (4) ◽  
pp. 141-145 ◽  
Author(s):  
Luca Luiselli ◽  
Godfrey C. Akani ◽  
Claudia Corti ◽  
Francesco M. Angelici
Keyword(s):  
Sexual Size Dimorphism ◽  
Dietary Habits ◽  
Prey Type ◽  
West African ◽  
Head Size ◽  
Size Dimorphism ◽  
Males And Females ◽  
Type 3 ◽  
Free Ranging ◽  
Food Niche

Sex-biased differences in dietary habits of snakes are often linked to pronounced sexual size dimorphism in absolute body size or in relative head size. We studied the food habits of free-ranging forest cobras (Naja melanoleuca) in southern Nigeria to find whether any intersexual dietary divergence is present in this species, and measured both museum vouchers and free-ranging specimens to find whether any intersexual divergence in relative head size is present. We demonstrated that: (1) head sizes increases more rapidly with SVL in females than in males, with a result that, at the same body length, the females tended to have significantly larger heads; (2) males and females were nearly identical in dietary habits, both if we consider prey size or prey type; (3) both sexes tended to prey upon relatively little sized preys. It is concluded that traditional evolutionary scenarios for explaining sexual dimorphism and food niche divergence are hardly valid in this case, and we need to look for entirely different hypotheses (e.g. linked to the sexual preference of males for females with larger heads).

Sexual dimorphism in cordylid lizards: a case study of the Drakensberg crag lizard, Pseudocordylus melanotus

1993 ◽  
Vol 71 (9) ◽  
pp. 1715-1723 ◽  
Author(s):  
P. le F. N. Mouton ◽  
J. H. van Wyk
Keyword(s):  
Sexual Dimorphism ◽  
Reproductive Activity ◽  
Energy Allocation ◽  
Head Size ◽  
Adult Males ◽  
Altitudinal Variation ◽  
Female Head ◽  
Basic Colour ◽  
Epidermal Glands

In a high-altitude population of the Drakensberg crag lizard, Pseudocordylus melanotus, most adult males, unlike adult females, are brightly coloured, and they are larger in body size and have relatively larger heads than females. Three basic colour phases can be distinguished among the brightly coloured adult males. No apparent differences in reproductive activity, number and differentiation state of the generation glands and femoral pores, or scar frequency were noted among the three colour phases. In males the development of bright colours and the differentiation of the epidermal glands coincide with the onset of sexual maturity. Sexual dimorphism in head size of adults is due to a decrease in female head size relative to juvenile head size as well as an increase in relative head size of males. Preliminary data indicate a social structure of territorial polygyny in P. melanotus and suggest that the dimorphism can partly be ascribed to sexual selection. There are also, however, indications of altitudinal variation in the expression of sexual dimorphism, which may be explained in terms of differential energy allocation by females at different altitudes.

Sexual dimorphism in trophic morphology and feeding behavior of wolf spiders (Araneae: Lycosidae) as a result of differences in reproductive roles

2002 ◽  
Vol 80 (4) ◽  
pp. 679-688 ◽  
Author(s):  
Sean E Walker ◽  
Ann L Rypstra
Keyword(s):  
Sexual Dimorphism ◽  
Feeding Behavior ◽  
Wolf Spider ◽  
Foraging Success ◽  
Wolf Spiders ◽  
Niche Divergence ◽  
Trophic Morphology ◽  
Males And Females ◽  
Almost All ◽  
The Relationship

Sexual dimorphism in animals is thought to be a result of differences between the sexes in the relationship between reproductive success and a trait, or a result of intersexual niche divergence. Intersexual niche divergence occurs as a result of competition between the sexes and is generally inferred from sexual dimorphism in morphological features associated with feeding. However, differences between the sexes in trophic morphology can be a result of either intersexual niche divergence or differences in the relationship between foraging success and reproduction between the sexes. In this study we examined sex differences in the trophic morphology of six wolf spider species and in the feeding behavior of two of these species. Females were larger than males in almost all characteristics even after differences in body size were accounted for, and killed and consumed more prey. We found little evidence of intersexual niche divergence based on differences in the relative prey sizes preferred by males and females of two species. Our data suggest that differences in the reproductive roles of males and females have resulted in foraging success being more important for female fitness than for male fitness and that differences in reproductive roles can result in sexual dimorphism.

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