The link between sexual dimorphism, activity budgets, and group cohesion: the case of the plains zebra (Equus burchelli)

2002 ◽  
Vol 80 (8) ◽  
pp. 1437-1441 ◽  
Author(s):  
P Neuhaus ◽  
K E Ruckstuhl
Keyword(s):  
Body Size ◽  
Reproductive Status ◽  
Sexually Dimorphic ◽  
Time Budgets ◽  
Activity Budgets ◽  
Equus Burchelli ◽  
Lactating Females ◽  
Males And Females ◽  
Reproductive Females ◽  
Dimorphic Species

Animals that differ in reproductive status and body size have different needs in terms of foraging and resting. In most social ungulates this leads to sexual segregation, probably because of incompatibilities between the activity budgets of males and females. Since most studies on behavioural differences between the sexes have been done on sexually dimorphic species, we decided to look at a system in which males and females are similar in body size. We studied time budgets, synchrony of behaviour, and bite rates of plains zebras (Equus burchelli) to evaluate the factors that enable these extremely social ungulates to stay in stable mixed-sex family groups throughout the year. As we predicted, time budgets were similar among males, lactating females, pregnant females, and non-reproductive females. Furthermore, we observed close synchronization of behaviours between females that differed in reproductive status and males. Lactating females, however, did take more bites per minute when foraging than either pregnant or non-reproducing females or males. We assume that the higher bite rates of lactating females were due to the extra costs of producing milk for their foal. We concluded that the special harem mating system, and for females the year-round possibility of conceiving, force the animals to synchronize their time budgets, which might be a major reason for the lack of difference in body size between males and females.

scholarly journals Sex identification in embryos and adults of Darwin’s finches

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0237687
Author(s):  
Mariya P. Dobreva ◽  
Joshua G. Lynton-Jenkins ◽  
Jaime A. Chaves ◽  
Masayoshi Tokita ◽  
Camille Bonneaud ◽  
...  
Keyword(s):  
Field Studies ◽  
Sexually Dimorphic ◽  
Genetic Studies ◽  
Darwin's Finches ◽  
Darwin’S Finches ◽  
Specific Morphology ◽  
Males And Females ◽  
Primer Sets ◽  
Dimorphic Species ◽  
Source Of Error

Darwin’s finches are an iconic example of adaptive radiation and evolution under natural selection. Comparative genetic studies using embryos of Darwin’s finches have shed light on the possible evolutionary processes underlying the speciation of this clade. Molecular identification of the sex of embryonic samples is important for such studies, where this information often cannot be inferred otherwise. We tested a fast and simple chicken embryo protocol to extract DNA from Darwin’s finch embryos. In addition, we applied minor modifications to two of the previously reported PCR primer sets for CHD1, a gene used for sexing adult passerine birds. The sex of all 29 tested embryos of six species of Darwin’s finches was determined successfully by PCR, using both primer sets. Next to embryos, hatchlings and fledglings are also impossible to distinguish visually. This extends to juveniles of sexually dimorphic species which are yet to moult in adult-like plumage and beak colouration. Furthermore, four species of Darwin’s finches are monomorphic, males and females looking alike. Therefore, sex assessment in the field can be a source of error, especially with respect to juveniles and mature monomorphic birds outside of the mating season. We caught 567 juveniles and adults belonging to six species of Darwin’s finches and only 44% had unambiguous sex-specific morphology. We sexed 363 birds by PCR: individuals sexed based on marginal sex specific morphological traits; and birds which were impossible to classify in the field. PCR revealed that for birds with marginal sex specific traits, sexing in the field produced a 13% error rate. This demonstrates that PCR based sexing can improve field studies on Darwin’s finches, especially when individuals with unclear sex-related morphology are involved. The protocols used here provide an easy and reliable way to sex Darwin’s finches throughout ontogeny, from embryos to adults.

TO SYNCHRONISE OR NOT TO SYNCHRONISE: A DILEMMA FOR YOUNG BIGHORN MALES?

Behaviour ◽  
1999 ◽  
Vol 136 (6) ◽  
pp. 805-818 ◽  
Author(s):  
Keyword(s):  
Body Size ◽  
Age Groups ◽  
Young Male ◽  
Ovis Canadensis ◽  
Sexually Dimorphic ◽  
Group Type ◽  
Group Members ◽  
Mixed Groups ◽  
Mixed Age ◽  
Dimorphic Species

AbstractBighorn sheep (Ovis canadensis) are sexually dimorphic and live in nursery groups, bachelor or mixed groups. To remain in a group, individuals have to synchronise their activity according to the type of group they are in, which may incur a cost for individuals of different body size from the other group members. To test this hypothesis, I calculated the degree of synchrony of activities for each individual within a group. Animals in nursery or bachelor groups were highly synchronised with each other while mixed-age-sex groups had the lowest group synchronisation index. Two and three-year old bighorn males are intermediate in body size between the two adult sexes. Two-year-old males always adjusted their behaviour independent of group type, while three-year-old males synchronised their behaviour when with bachelor, but less so when in nursery groups. I suggest that two- and three-year-old males may face a conflict between synchronising their behaviour to stay in a group and the need to forage according to their own time budgets. I conclude that intermediate-sized young male ungulates of sexually dimorphic species may be better off forming same-sex-age groups.

Sexual segregation in bison: a test of multiple hypotheses

Behaviour ◽  
2005 ◽  
Vol 142 (7) ◽  
pp. 897-927 ◽  
Author(s):  
Eric W. Schaad ◽  
David S. Wiseman ◽  
Royce R. Huber ◽  
Michael S. Mooring ◽  
Dominic D. Reisig ◽  
...  
Keyword(s):  
Body Size ◽  
Predation Risk ◽  
Sexual Segregation ◽  
Bison Bison ◽  
Sexually Dimorphic ◽  
Activity Budgets ◽  
Single Sex ◽  
Multiple Hypotheses ◽  
Mixed Groups ◽  
Large Groups

AbstractSexual segregation, in which males and females form separate groups for most of the year, is common in sexually dimorphic ungulates. We tested multiple hypotheses to explain sexual segregation in bison (Bison bison) at National Bison Range, Montana and Fort Niobrara National Wildlife Refuge, Nebraska during June-August of 2002-2003. Fieldwork involved use of GPS to record space use by segregated groups, vegetation transects to measure forage availability, fecal analyses to document diet composition and quality, and behavioural observations to characterize activity budgets. During sexual segregation, males in bull groups used areas with greater per capita abundance of forage, higher proportion of weeds, and less nutritious grasses (as indicated by lower % fecal nitrogen) compared with females in cow or mixed groups. However, there was no difference between the sexes in activity budgets, predation risk factors, or distance to water. Single-sex bull groups were no more synchronized in activity than mixed groups. These results support the 'sexual dimorphism-body size hypothesis', which proposes that males segregate from females because their larger body size requires more abundant forage, while longer ruminal retention permits efficient use of lower-quality forage. The gastrocentric model, based on the digestive physiology and foraging requirements of dimorphic ungulates, supplies the most likely proximate mechanism for bison sexual segregation. Our results would also partly support the 'reproductive strategy-predation risk hypothesis' if females form large groups to reduce predation risk. The predictions of the 'activity budget hypothesis' were not supported for bison.

Sexual dichromatism in the marbled salamander, Ambystoma opacum

2007 ◽  
Vol 85 (9) ◽  
pp. 1008-1013 ◽  
Author(s):  
Brian D. Todd ◽  
Andrew K. Davis
Keyword(s):  
Body Size ◽  
Surface Area ◽  
Relative Proportion ◽  
Dorsal Surface ◽  
Sexual Dichromatism ◽  
Sexually Dimorphic ◽  
Ambystoma Opacum ◽  
Males And Females ◽  
Marbled Salamander ◽  
Image Analysis Techniques

Reports of sexual dichromatism in salamanders are rare and have been generally restricted to a few species in the families Hynobiidae and Salamandridae. We used image analysis techniques to examine sexual dichromatism in the marbled salamander, Ambystoma opacum (Gravenhorst, 1807). We measured the average hue of white saddles on male and female marbled salamanders (n = 118), as well as the proportion of white dorsal surface area relative to the black dorsal surface area, to determine the extent of sexual dichromatism in this species. We also tested whether patterning and coloration were correlated with body size or relative body mass. Males had significantly whiter saddles and higher relative proportions of white coloration on their dorsal surfaces than did females. Furthermore, the relative proportion of white areas on the dorsum was positively correlated to body condition in both males and females. Body size was not correlated with hue or proportion of white area on the dorsum. To our knowledge, we report the first confirmation of sexually dimorphic coloration in the ambystomatid salamander family, extending the known distribution of sexual dichromatism in the order Caudata.

Mortality patterns in a protected population of isards (Rupicapra pyrenaica)

2001 ◽  
Vol 79 (11) ◽  
pp. 2072-2079 ◽  
Author(s):  
Georges Gonzalez ◽  
Jean-Paul Crampe
Keyword(s):  
Mortality Rates ◽  
Sexually Dimorphic ◽  
Large Herbivores ◽  
Rupicapra Pyrenaica ◽  
Type Pattern ◽  
Males And Females ◽  
Stationary Type ◽  
Pyrenean Chamois ◽  
Dimorphic Species ◽  
Winter Severity

We considered variation in mortality over 8 years in a protected population of isards (Pyrenean chamois; Rupicapra pyrenaica) within the Pyrenean National Park using monthly systematic skull collection. After testing the stationary-type pattern of estimates of mortality of the living population, we (i) analysed the composition of a sample of dead animals in terms of age and sex; (ii) investigated temporal patterns of mortality and their relationship with winter severity; (iii) tested for sexual differences in mortality rates in this weakly sexually dimorphic species. Of 588 animals found dead from natural causes, 114 were kids (19.4%). No statistical differences existed in the composition of the sample according to sex (the ratio of males to females was 1/1.13). Age at death did not differ significantly between the sexes or among years. A positive relationship was found between winter severity (expressed as cumulative snowfall) and mortality rates for both kids and adults. During mild winters, the mortality rate was low (a mean of 38.4 carcasses per year versus 124 per year in severe winters) and was concentrated on the oldest animals, mainly males. Based on 303 skulls more than 1 year old, annual survivorship curves revealed a period of low mortality (prime age) extending to 9 and 10 years of age for males and females, respectively, followed by a period of increasing mortality (senescence). Our results are commented on in light of recent publications on the demography of populations of large herbivores.

scholarly journals Differences in Pelvic Fin Length Represent Sexual Dimorphism in Utah Chub (Gila atraria)

2014 ◽  
Vol 7 (1) ◽  
pp. 42-45 ◽  
Author(s):  
Mark C. Belk ◽  
Scott Bird ◽  
Mehmet Cemal Oguz ◽  
Jerald B. Johnson
Keyword(s):  
Body Size ◽  
Sexual Dimorphism ◽  
Cyprinid Fish ◽  
Sexually Dimorphic ◽  
Adaptive Function ◽  
Males And Females ◽  
The Difference ◽  
Sexually Mature ◽  
Fin Length ◽  
Pelvic Fin

The cyprinid fish Gila atraria Girard (Utah chub) is generally considered a sexually monomorphic species. However, prior observations revealed variation in pelvic fin length within populations that appears sexually dimorphic. We measured the relative pelvic fin length of 419 sexually mature Utah chub from 8 different locations to determine the magnitude and generality of this apparent dimorphism. Pelvic fin length in G. atraria differs between sexes by about 10% on average; males have longer pelvic fins than females. The dimorphism is general across all locations, but it is not related to body size. Magnitude of the dimorphism varies by predation environment – the difference between males and females is slightly greater in low predation environments. We find no evidence for an adaptive function for this dimorphism; however, it does provide an efficient mechanism for determining sex without dissection.

scholarly journals Allometry and morphological trait relationship in the sexually dimorphic Chinese dobsonfly, Acanthacorydalis asiatica (Wood-Mason, 1884) (Megaloptera, Corydalidae)

ZooKeys ◽  
2019 ◽  
Vol 854 ◽  
pp. 119-129
Author(s):  
Chengquan Cao ◽  
Pei Yu ◽  
Fumio Hayashi
Keyword(s):  
Body Size ◽  
Male Genitalia ◽  
Wing Length ◽  
The Body ◽  
Sexually Dimorphic ◽  
Male Body ◽  
Male Body Size ◽  
Intermediate Size ◽  
Mandible Length ◽  
Dimorphic Species

Male insects with large weapons such as horns and elongate mandibles would be expected to invest more on such structures than other parts of the body for advantages in male to male competition for mating. In male genitalia, however, intermediate size provides a better fit for more females than small or large sizes, and such a male would leave more offspring regardless of their body size. These predictions were tested using a static allometry analysis between body size and other trait sizes. Acanthacorydalisasiatica is a large dobsonfly (Megalotera) and males have conspicuously large mandibles used as weapons. We examined the hypothesis that the male mandibles of this sexually dimorphic species are sexually selected to enlarge, whereas the male genitalia are stable to be intermediate regardless of a great variation in body size. The results, as predicted, showed positive allometry between male body size and mandible length but negative allometry between male body size and ectoproct length (a male grasping structure). Sperm are transferred through a small spermatophore attached externally to the female genital opening, so it may be evolutionarily unnecessary to develop an enlarged male genital size. In contrast, there may be a trade-off between male mandible size and wing length, because of negative allometry between body size and wing length in males but isometry between them in females.

Diving behaviour of male and female western grebes

1988 ◽  
Vol 66 (12) ◽  
pp. 2695-2698 ◽  
Author(s):  
L. Scott Forbes ◽  
Spencer G. Sealy
Keyword(s):  
British Columbia ◽  
Body Size ◽  
Water Depth ◽  
Wave Action ◽  
Diving Behaviour ◽  
Sexually Dimorphic ◽  
Habitat Conditions ◽  
Male And Female ◽  
Males And Females

We studied diving in western grebes (Aechmophorus occidentalis), which are sexually dimorphic, at Duck and Kootenay lakes in southeastern British Columbia to determine if differences in sex, and hence body size, resulted in differences in behaviour. Springing dives were used more frequently in deeper water and when wave action was higher, but there were no clear differences between males and females. As well, the dive–pause regressions for males and females did not differ. We conclude that differences in body size are not important determinants of diving behaviour in western grebes, but that habitat conditions (e.g., water depth, wave action) are.

scholarly journals Sex identification in embryos and adults of Darwin’s finches

2020 ◽  
Author(s):  
Mariya P. Dobreva ◽  
Joshua G. Lynton-Jenkins ◽  
Jaime A. Chaves ◽  
Masayoshi Tokita ◽  
Camille Bonneaud ◽  
...  
Keyword(s):  
Field Studies ◽  
Sexually Dimorphic ◽  
Genetic Studies ◽  
Darwin's Finches ◽  
Darwin’S Finches ◽  
Specific Morphology ◽  
Males And Females ◽  
Primer Sets ◽  
Dimorphic Species ◽  
Source Of Error

AbstractDarwin’s finches, endemic to the Galapagos and Cocos islands, are an iconic example of adaptive radiation and evolution under natural selection. Comparative genetic studies using embryos of Darwin’s finches have shed light on the possible evolutionary processes underlying the speciation of this clade. Molecular identification of the sex of embryonic samples is important for such studies, where this information often cannot be inferred otherwise. We tested a fast and simple chicken embryo protocol for extraction of genomic DNA on Darwin’s finch embryos. In addition, we suggest modifications to two of the previously reported PCR primer sets for CHD1, a gene used for sexing in adult passerine birds. The sex of all 29 tested embryos of six species of Darwin’s finches was determined successfully by PCR, using both primer sets. Hatchlings/nestlings and fledglings are also impossible to distinguish visually. This includes juveniles of sexually dimorphic species which are yet to moult in adult-like plumage and beak colouration. Furthermore, four species of Darwin’s finches are monomorphic, males and females looking alike. Therefore, sex assessment in the field can be a source of error, especially with respect to juveniles and mature monomorphic birds outside of the mating season. We caught 567 juveniles and adults belonging to six species of Darwin’s finches and only 44% had unambiguous sex-specific morphology. We sexed 363 birds by PCR, including individuals sexed based on marginal sex specific morphological traits (N=278) and birds which were impossible to classify in the field (N=39). For birds with marginal sex specific traits, PCR results revealed a 13% sexing error rate. This demonstrates that PCR based sexing can improve field studies on Darwin’s finches, especially when individuals with unclear sex-related morphology are involved. The protocols used here provide an easy and reliable way to sex Darwin’s finches throughout ontogeny, from embryos to adults.

Disrupting information alters the behavioral response to a mutual signal trait in both sexes of Nicrophorus (Coleoptera: Silphidae) burying beetles

2019 ◽  
Vol 30 (4) ◽  
pp. 960-967
Author(s):  
Jillian D Wormington ◽  
Barney Luttbeg
Keyword(s):  
Body Size ◽  
Behavioral Responses ◽  
Reproductive Investment ◽  
Sexually Dimorphic ◽  
Burying Beetles ◽  
Signaling Function ◽  
Opposite Sex ◽  
Nicrophorus Orbicollis ◽  
Males And Females ◽  
Competition For Resources

AbstractEffective signals transfer information in a way that enhances the fitness of the sender. Signal traits are often sexually dimorphic. However, in some species, males and females display similar signals, and these mutual signals are less often studied. Competition for resources occurs in both males and females, and mate choice is likely to occur whenever mates vary in quality and reproductive investment is high. Nicrophorus burying beetles compete intrasexually over the carrion resources on which they biparentally raise their young. Nicrophorus species also often have clypeal membranes which scale hyperallometrically with body size, exaggerating the apparent body size of larger individuals. To examine the potential signaling function of clypeal membranes, we examined the behavioral responses of male and female Nicrophorus orbicollis and Nicrophorus pustulatus burying beetles to same- and opposite-sex social partners which had their membranes painted black or clear. We found evidence that blocking the information in clypeal membranes affected intrasexual aggressive interactions for both sexes of both species. Blocking a female’s signal reduced the likelihood of mating attempts for male N. pustulatus, whereas blocking a male’s signal influenced female rejection behaviors in N. orbicollis. Our results show that males and females can experience similar selection pressures, and suggest that examining mutual signals in a broader range of systems will expand our understanding of evolutionary differences and similarities between the sexes.

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