The evolution of sexual dimorphism in the skink Eumeces laticeps: an example of sexual selection

1985 ◽  
Vol 63 (5) ◽  
pp. 995-1002 ◽  
Author(s):  
Laurie J. Vitt ◽  
William E. Cooper Jr.
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Breeding Season ◽  
Prey Size ◽  
Maximum Size ◽  
Head Size ◽  
Sexually Dimorphic ◽  
Eumeces Laticeps ◽  
Aggressive Male ◽  
The Mean

Adults of the skink Eumeces laticeps are sexually dimorphic in coloration, body size, head size, and relative head size. Males have larger heads at a given body size than females and the divergence in relative head size is coincident with the size at which sexual maturity is reached. Although there were no differences between sexes in tail loss frequencies, there were substantial differences in frequencies of body and head scars, a consequence of aggressive male–male interactions. Prey size was correlated with body and head size and males tended to eat larger prey items than females. However, both sexes are capable of eating prey much larger than the mean or maximum size of prey found in stomachs, suggesting that resource partitioning is a consequence of sexual size differences rather than a cause. The heads of males at a given body size increase during the breeding season, and a combination of head and body size apparently determines the outcome of intrasexual aggressive encounters. Moreover, small males were never observed with females during the breeding season, and those males observed "guarding" females were significantly larger than males observed in the absence of females. We conclude that sexual selection accounts for many of the differences in morphological traits between sexes of E. laticeps.

The effect of body size and body condition on the ovulation rate of ewes

1977 ◽  
Vol 24 (3) ◽  
pp. 377-385 ◽  
Author(s):  
M. J. Ducker ◽  
J. S. Boyd
Keyword(s):  
Body Size ◽  
Breeding Season ◽  
Body Condition ◽  
Live Weight ◽  
Ovulation Rate ◽  
Subjective Measure ◽  
Body Dimensions ◽  
The Mean ◽  
Per Se ◽  
Linear Body

SUMMARYBody size was estimated for 255 Greyface ewes using five linear body dimensions. On the basis of this calculated measure combined with a subjective measure of body size 50 small and 50 large ewes were selected for use in the experiment. Precise ovulation data were obtained by endoscopy and this technique allowed the ewes to be mated subsequently.Body size did not affect the mean ovulation rate of the ewes although, at the same level of body condition, the large ewes were 25% heavier than the small ewes. The ovulation rates and the numbers of lambs born were influenced by changes in live weight and body condition. For these reasons live weight per se was not a good indicator of ovulation rate as ewe live weight was a combination of both body size and body condition. At the same live weight small ewes in improving body condition had a significantly higher ovulation rate than large ewes in reducing body condition.The onset of the breeding season of the ewes was not affected by their body size. The mean date of onset of oestrous activity for both large and small ewes was 17 October 1972 at a latitude 55° 52′ N.

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.

The manifestation and significance of sexual dimorphism in anguid lizards: a case study of Barisia monticola

1989 ◽  
Vol 67 (1) ◽  
pp. 68-72 ◽  
Author(s):  
James L. Vial ◽  
James R. Stewart
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Reproductive Behavior ◽  
Reproductive Potential ◽  
Head Size ◽  
Adult Males ◽  
Allometric Growth ◽  
Natural And Sexual Selection ◽  
Dimorphic Expression

The dimorphic expression of body size, body – head size relationships, and chromatic characters among anguid lizards is reviewed. These characteristics are quantitatively examined in a population of Barisia monticola. No sexual differences are found in body size. Head size is positively correlated with body size; however, allometric growth rates in head size are significantly greater in adult males than in females or juveniles. Adult males also differ significantly in eight of nine chromatic characters, the most pronounced being the presence of light dorsal scale markings. These differences are explored in the context of both natural and sexual selection. We hypothesize that the absence of dimorphism in overall body size is the result of natural selection operating to maximize female reproductive potential. In contrast, we predict that dimorphism expressed in body – head size relationships and dichromatism are consequences of sexual selection relating to agonistic and reproductive behavior of males.

Activity area during the breeding season of Varanus gouldii (Reptilia : Varanidae) in an urban environment.

1994 ◽  
Vol 21 (6) ◽  
pp. 633 ◽  
Author(s):  
G Thompson
Keyword(s):  
Body Size ◽  
Urban Environment ◽  
Leaf Litter ◽  
Breeding Season ◽  
Western Australia ◽  
Activity Area ◽  
Mean Size ◽  
The Mean ◽  
Activity Areas

The activity area of ten Varanus gouldii in Karrakatta Cemetery, Perth, Western Australia, was measured by daily locations obtained by telemetry, during the breeding season (October-December) in 1992. The mean size of activity area was 8.91 ha; activity area was positively correlated with body size. There were significant overlaps in activity areas and no evidence of territoriality for male or female V. gouldii. The animals often foraged in areas of dense leaf litter near the periphery of their activity area and retreated to burrows that were more centrally located.

Reproduction in a laboratory colony of the marsupial mouse Sminthopsis larapinta (Mardupialia : Dasyuridae)

1969 ◽  
Vol 17 (4) ◽  
pp. 637 ◽  
Author(s):  
GK Godfrey
Keyword(s):  
Breeding Season ◽  
Maximum Size ◽  
Urogenital Sinus ◽  
Corpora Lutea ◽  
Young Females ◽  
The Third ◽  
Laboratory Colony ◽  
The Mean ◽  
Mean Cycle ◽  
North Western

A laboratory colony of S. larapinta was established with three females and four males received from north-western Queensland. Over a period of two and a half years 109 young were born and second-generation descendants were produced. In the third breeding season oestrous cycles were irregular and, in the few instances where copulation was recorded, this was associated with almost 100% prenatal mortality. The colony became extinct without the cause being definitely established. In Adelaide S. larapinta had a well-defined breeding season with all females either pregnant or in oestrus from July to February. From March until June all the females were in anoestrus. The males produced sperm throughout the year. A technique was developed for determining the length of the oestrous cycle, based upon the incidence of epithelial cells in the urine. S. larapinta is polyoestrous, with a mean cycle length of 26.25�0.5 days. Gestation occupies 12.5 days, and a maximum of eight young remain in the pouch, attached to the teats, for 40 days. They are suckled in the nest for a further 30 days. Weaning takes place at 70 days, and the young females come into oestrus from 4 months of age onwards. Twenty female reproductive tracts were sectioned and examined and the anatomy and histology described briefly. The mean number of ova shed per ovulation was 30.6 (n = 12) with one instance of 40. The corpora lutea are formed rapidly, and reach their maximum size towards the end of pregnancy. They have completely regressed by the seventh week of lactation. The young are born through a pseudovaginal canal which extends from the median vagina to the urogenital sinus. This closes within 24-48 hr of parturition. The high "pre-pouch" and litter mortality observed during this study is discussed.

Ecology and evolution of sympatric sticklebacks (Gasterosteus): specialization for alternative trophic niches in the Enos Lake species pair

1984 ◽  
Vol 62 (11) ◽  
pp. 2280-2286 ◽  
Author(s):  
P. Bentzen ◽  
J. D. McPhail
Keyword(s):  
Body Size ◽  
Standard Length ◽  
Feeding Behaviour ◽  
Prey Size ◽  
Distinct Species ◽  
Fixed Time ◽  
Threespine Stickleback ◽  
Sexually Dimorphic ◽  
Species Pair ◽  
Trophic Niches

Two morphologically distinct species of threespine stickleback (Gasterosteus) coexist in Enos Lake on Vancouver Island. For convenience these species are referred to as "limnetics" and "benthics." We used three experiments to compare the feeding performance of the two species and to test the hypothesis that limnetics are adapted for planktivory whereas benthics are adapted to forage on substrates. The results support this conclusion. When tested for maximum prey size; benthics consumed larger prey (relative to their body size) than limnetics. Benthics also were more successful than limnetics in foraging on a substrate. When allowed to forage for a fixed time on a detritus substrate, benthics of both sexes captured more prey than male limnetics, even though male limnetics directed as many feeding strikes at the substrate as did the benthics. Female limnetics would not forage on a detritus substrate. Limnetics were more successful in feeding on plankton than benthics. When held in mesh enclosures suspended in Enos Lake, limnetics consumed more plankton than benthics. Small limnetics (26–36 mm standard length) consumed nearly four times more plankton than large limnetics (44–50 mm standard length). The small limnetics were all either mature females or immature males; the large limnetics were all mature males. The results of the benthic foraging and plankton feeding comparisons support the additional conclusion that Enos Lake limnetics are sexually dimorphic in their feeding behaviour.

Differences in sexual dimorphism among four gazelle taxa (Gazella spp.) in the Middle East

2010 ◽  
Vol 60 (4) ◽  
pp. 395-412 ◽  
Author(s):  
Peter Cunningham ◽  
Martin Plath ◽  
Torsten Wronski ◽  
Mohamed Sandouka
Keyword(s):  
Body Weight ◽  
Sexual Selection ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Mating Systems ◽  
Research Centre ◽  
Sexually Dimorphic ◽  
Male Sex ◽  
The Difference ◽  
Horn Development

AbstractSexual selection can lead to sexual dimorphism, where elaborated traits used in mate attraction or weaponry are more expressed in the male sex. The degree of sexual dimorphism, however, is known to vary even among closely related taxa. Here we examined sexual dimorphism in horn length and three measures related to body size (body weight, shoulder height, and neck circumference) in four gazelle taxa, representing at least three species, i.e. Dorcas gazelle (G. dorcas), Sand gazelle (G. subgutturosa marica) and Mountain gazelle (G. gazella). The latter is represented by two distinctive phenotypes maintained and bred at the King Khalid Wildlife Research Centre in Saudi Arabia. We describe marked differences in sexual dimorphism among taxa. For example, the difference in sexually dimorphic horn development was driven primarily by females exhibiting pronounced differences in horn development. We discuss how divergent mating systems, and group sizes affect these differences among the examined taxa, with more competition in larger groups probably promoting the evolution of larger horns in females, thereby leading to less sexual dimorphism.

Sign in / Sign up

Export Citation Format

Share Document