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Large Males (large + male)
Terms modified by Large Males Selected AbstractsDescription of a new cichlid fish species of the genus Benthochromis (Perciformes: Cichlidae) from Lake TanganyikaJOURNAL OF FISH BIOLOGY, Issue 3 2008T. Takahashi Benthochromis horii, a new cichlid species is described based on 19 type specimens from the deep waters of Lake Tanganyika. It differs from its congeners by having smaller eyes and longer snout (eye length usually shorter than snout length v. equal to or longer than snout length in Benthochromis tricoti and Benthochromis melanoides), and more dorsal fin rays (total number of spines and soft rays in dorsal fin usually 30 or 31 v. usually 28 or 29 in B. tricoti and B. melanoides). Large males of the new species differ from those of congeneric species in terms of their body colour pattern and long pelvic fins. This species has been confused with B. tricoti and has been traded as an aquarium fish. [source] Sexual segregation in western grey kangaroos: testing alternative evolutionary hypothesesJOURNAL OF ZOOLOGY, Issue 2 2007A. M. MacFarlane Abstract In sexually dimorphic ungulates, sexual segregation is hypothesized to have evolved because of sex-specific differences in body size and/or reproductive strategies. We tested these alternative hypotheses in kangaroos, which are ecological analogues of ungulates. Kangaroos exhibit a wide range of body sizes, particularly among mature males, and so the effects of body size and sex can be distinguished. We tested predictions derived from these hypotheses by comparing the distribution of three sex,sex size classes of western grey kangaroos Macropus fuliginosus, in different habitats, and the composition of groups of kangaroos, across seasons. In accordance with the predation risk-reproductive strategy hypothesis, during the non-breeding season, females, which were more susceptible to predation than larger males, and were accompanied by vulnerable young-at-foot, were over-represented in secure habitats. Large males, which were essentially immune to predation, occurred more often than expected in nutrient-rich habitat, and small males, which faced competing demands of predator avoidance and feeding, were intermediate between females and large males in their distribution across habitats. During the breeding season, females continued to be over-represented in secure habitats when their newly emerged pouch young were most vulnerable to predation. All males occupied these same habitats to maximize their chances of securing mates. Consistent with the social hypotheses, groups composed of individuals of the same sex, irrespective of body size, were over-represented in the population during the non-breeding season, while during the breeding season all males sought females so that mixed-sex groups predominated. These results indicate that body size and reproductive strategies are both important, yet independent, factors influencing segregation in western grey kangaroos. [source] Can the limited marsupium space be a limiting factor for Syngnathus abaster females?JOURNAL OF ANIMAL ECOLOGY, Issue 2 2008Insights from a population with size-assortative mating Summary 1Some syngnathid species show varying degrees of sex role reversal aside from male pregnancy, with females competing for access to mates and sometimes presenting conspicuous secondary sexual characters. Among other variables, brooding space constraints are usually considered a key element in female reproductive success, contributing strongly to the observed morphological and behavioural sexual differences. Nevertheless, a close relationship between sex role reversal and male brooding space limitation has not yet been accurately demonstrated in field studies. 2The present work, conducted over two consecutive breeding seasons in a wild population of the sex role-reversed pipefish Syngnathus abaster, simultaneously analysed egg number and occupied space, as well as the free area in the male's marsupium. The number of eggs that would fit in the observed unoccupied space was estimated. 3Contrary to what would be expected, given the marked sexual dimorphism observed in the population studied, where females were larger and more colourful, male brooding space did not appear to limit female reproduction as neither large nor small individuals presented a fully occupied pouch. Interestingly, the largest unoccupied areas of marsupium were found in the larger individuals, although they received more and larger eggs. Laboratory data also showed that larger females lay larger eggs. 4Together, these results suggest the existence of assortative mating, which may result from: (i) the reluctance of larger males (which tend not to receive small eggs usually laid by small females) to mate with lower quality females, even at the expense of a smaller number of offspring; or (ii) female,female competition, which might strongly reduce the hypothesis of a small female mating with a large male. The potential impact of temperature on reproduction and population dynamics is also discussed in the light of ongoing climatic changes. [source] Sexual size dimorphism in the two spot ladybird beetle Adalia bipunctata: developmental mechanism and its consequences for matingECOLOGICAL ENTOMOLOGY, Issue 4 2002Hironori Yasuda Abstract ,1. The literature on ladybirds indicates that males are consistently smaller than females but take the same length of time to complete their development. Rearing Adalia bipunctata at 20 and 25 °C confirmed that protandry cannot account for sexual size dimorphism in this species, nor can a difference in egg size. 2. Female larvae consumed more food and had a higher relative growth rate in the fourth instar than did male larvae. 3. When food is limited, small males appear to be more successful at mating than are large males. 4. To account for these results, it is hypothesised that the gonads of male larvae compete more strongly with the soma for resources and that this reduces the growth potential of the soma of male larvae relative to that of female larvae. The greater mating success of small males when food is limited supports the eat or mate hypothesis, which predicts that when food is limited small males will spend less time feeding and more time mating than will large males. [source] Mate discrimination by females in the burying beetle Nicrophorus orbicollis: the influence of male size on attractiveness to femalesECOLOGICAL ENTOMOLOGY, Issue 1 2002Andria E. Beeler Summary 1. Female burying beetles behave differently towards males of different sizes, avoiding mating with large males that are not defending resources but mating with small males regardless of the presence of resources. Females of the burying beetle Nicrophorus orbicollis were therefore examined to determine whether they discriminate among males using only pheromonal signals. The influence of female size on its own mate choice was also examined. 2. Females do use male pheromonal signals to discriminate among males and these signals do appear to convey information about male body size to females. Overall, females were more likely to be attracted to larger males than to smaller males. 3. Female choice of a male was influenced by both the female's own body size and the size of the female relative to the size of the two males available to it. 4. While there is an overall mating advantage for larger males, resulting from female preferences based on odour cues, smaller males are also attractive to some females under some circumstances. 5. It is argued that there are different costs and benefits of mating with different sized males, leading to the evolution of context-dependent mate choice for females and the need to be able to discriminate males of different sizes from a distance. [source] Female Mate Choice, Calling Song and Genetic Variance in the Cricket, Gryllodes sigillatusETHOLOGY, Issue 3 2008Jocelyn Champagnon Female preferences for song patterns of males of Gryllodes sigillatus and genetic variance of morphological traits correlated with them were analyzed. Females preferred short pulses associated with large males. The males' thorax width, wing length and femur III length showed stronger relationship with the song pulse duration, whereas the relationship between pulse duration and wing width was not significant. Interestingly, this last trait was the only one that showed significant levels of genetic variance. Perhaps these results could be explained by the evolutionary response to sexual selection. Sexual selection could deplete the genetic variance in the male traits related to male-mating success. [source] Female Choice, Female Reluctance to Mate and Sexual Selection on Body Size in the Dung Fly Sepsis cynipseaETHOLOGY, Issue 7 2000Wolf U. Blanckenhorn We investigated the mechanisms of sexual selection in the common dung fly Sepsis cynipsea and how these affect selection on body size at the population level. Because of the presumed costs associated with mating, we predicted that there would be a decrease in the general reluctance of females to mate with any particular male at higher male densities at the mating site, a fresh cow pat, resulting in indirect female choice and a decrease in the strength of sexual selection. In contrast, classical direct female choice and male-male competition should result in increased selection intensities because more opportunities for choice and competition exist at higher densities. Female reluctance to mate and female assessment of males are expressed in prominent female behaviour to repel mates in several insect species, including S. cynipsea. Laboratory pair-wise choice experiments showed that large males were more likely to obtain copulations, which also ensued more promptly, suggesting female assessment of male quality (direct female choice). There was a basic influence of male activity but little further effect of male scramble competition on the outcome of mating. Another laboratory experiment showed a decrease in female shaking duration per male, associated with an asymptote in the shaking duration per female, as male density and harassment increased, but did not show the increase in mating frequency predicted by the female reluctance hypothesis. A study estimating sexual selection differentials in the field showed that directional selection for larger males was present overall and was negatively related to seasonally mediated variation in male density. Our study suggests that direct female choice in combination with indirect female choice (due to an interaction of female reluctance to mate and male persistence) is most consistent with the behavioural and selection patterns observed in S. cynipsea, but male effects cannot be definitively excluded. [source] GENETIC VARIATION IN MALE EFFECTS ON FEMALE REPRODUCTION AND THE GENETIC COVARIANCE BETWEEN THE SEXESEVOLUTION, Issue 6 2003MARY ELLEN CZESAK Abstract., Males of many insect species increase the fecundity and/or egg size of their mates through the amount or composition of their nuptial gifts or ejaculate. The genetic bases of such male effects on fecundity or egg size are generally unknown, and thus their ability to evolve remains speculative. Likewise, the genetic relationship between male and female investment into reproduction in dioecious species, which is expected to be positive if effects on fecundity are controlled by at least some of the same genes in males and females, is also unknown. Males of the seed beetle Stator limbatus contribute large ejaculates to females during mating, and the amount of donated ejaculate is positively correlated with male body mass. Females mated to large males lay more eggs in their lifetime than females mated to small males. We describe an experiment in which we quantify genetic variation in the number of eggs sired by males (mated to a single female) and found that a significant proportion of the phenotypic variance in the number of eggs sired by males was explained by their genotype. Additionally, the number of eggs sired by a male was highly positively genetically correlated with his body mass. The between-sex genetic correlation, that is, the genetic correlation between the number of eggs sired by males and the number of eggs laid by females, was highly positive when eggs were laid on Acacia greggii seeds. This indicates that males that sire many eggs have sisters that lay many eggs. Thus, some of the genes that control male ejaculate size (or some other fecundity-enhancing factor) when expressed in males appear to control fecundity when expressed in females. We found no significant interaction between male and female genotype on fecundity. [source] Male body size predicts sperm number in the mandarinfishJOURNAL OF ZOOLOGY, Issue 3 2010M. B. Rasotto Abstract Theory predicts that, in species with non-resource-based mating systems, female preference for male sexual traits might be selected to ensure higher levels of fertility. Accordingly, secondary sexual traits used by females to assess males are expected to covary with ejaculate size and/or quality transferred during copulation, and female fecundity should be directly linked to mating with more attractive males. To date, direct tests of this hypothesis have been performed on internal fertilizing species, where several factors, such as for instance sperm competition, cryptic female choice, male parasite load, may affect ejaculate characteristics and female fecundity. Here, we used as a model the mandarinfish Synchiropus splendidus a small pelagic spawner where males only provide females with ejaculates and sperm competition does not occur. Males are significantly larger than females and we experimentally demonstrated that females prefer larger males. In addition, by collecting gametes from 67 natural spawning events, we attained a measure of the number of eggs and sperm released in each spawning event and the fertilization rates. The mean number of gametes produced positively correlates with body size in both sexes. Males do not regulate sperm number according to egg number and/or female body size. Fertilization success is significantly related to the mean number of sperm released but not directly to male body size. These findings, despite not fully accomplishing theoretical expectation, suggest that larger and more fecund females may suffer sperm limitation in mating with smaller males. In addition, our results have possible implications for the aquarium fishery of this species, which targets large males. [source] Sexual segregation in western grey kangaroos: testing alternative evolutionary hypothesesJOURNAL OF ZOOLOGY, Issue 2 2007A. M. MacFarlane Abstract In sexually dimorphic ungulates, sexual segregation is hypothesized to have evolved because of sex-specific differences in body size and/or reproductive strategies. We tested these alternative hypotheses in kangaroos, which are ecological analogues of ungulates. Kangaroos exhibit a wide range of body sizes, particularly among mature males, and so the effects of body size and sex can be distinguished. We tested predictions derived from these hypotheses by comparing the distribution of three sex,sex size classes of western grey kangaroos Macropus fuliginosus, in different habitats, and the composition of groups of kangaroos, across seasons. In accordance with the predation risk-reproductive strategy hypothesis, during the non-breeding season, females, which were more susceptible to predation than larger males, and were accompanied by vulnerable young-at-foot, were over-represented in secure habitats. Large males, which were essentially immune to predation, occurred more often than expected in nutrient-rich habitat, and small males, which faced competing demands of predator avoidance and feeding, were intermediate between females and large males in their distribution across habitats. During the breeding season, females continued to be over-represented in secure habitats when their newly emerged pouch young were most vulnerable to predation. All males occupied these same habitats to maximize their chances of securing mates. Consistent with the social hypotheses, groups composed of individuals of the same sex, irrespective of body size, were over-represented in the population during the non-breeding season, while during the breeding season all males sought females so that mixed-sex groups predominated. These results indicate that body size and reproductive strategies are both important, yet independent, factors influencing segregation in western grey kangaroos. [source] Morphology and reproduction of Nipponomysella subtruncata (Yokoyama), a galeommatoidean bivalve commensal with the sipunculan Siphonosoma cumanense (Keferstein) in JapanJOURNAL OF ZOOLOGY, Issue 4 2001J. Lützen Abstract The shell and anatomy of Nipponomysella subtruncata is described. The bivalve is attached singly or in groups of up to nine on Siphonosoma cumanense, a burrowing intertidal sipunculan in south-west Japan. The species is a protandrous hermaphrodite. Specimens 1.4,2.5 mm long are males, which between 2.1 and 3 mm in length reverse sex and remain females. Reproduction peaks in summer and the annual number of clutches is small. Ripe oocytes, 84,88 ,m diameter, are spawned into the suprabranchial cavity where they develop into 107-,m-long straight-hinged veligers. Following a planktotrophic period of unknown duration, the c. 360-,m-long spat normally settle upon and attach to the shells of larger, predominantly female, individuals. At a length of 1,1.6 mm they detach again and live separately thereafter. Sperm are transferred in spermatophores and stored within paired, mushroom-shaped receptacles located posteriorly in the female's suprabranchial cavity. The receptacles first appear in large males or in specimens in the process of reversing sex. Stored sperm probably survive long enough to fertilize more than one clutch. The anatomy of Nipponomysella is characteristic of the Montacutidae, and is of especial interest because of the unique structure of the sperm receptacles. [source] Size variation and mating success in the stag beetle, Lucanus cervusPHYSIOLOGICAL ENTOMOLOGY, Issue 3 2006DEBORAH J. HARVEY Abstract The stag beetle, Lucanus cervus, is Britain's largest beetle, with a patchy distribution in southern England. The literature suggests that it displays exceptional size variation, particularly in the males, but no analysis of size inequality has ever been conducted. In the present study, stag beetle adults are measured and allometric relationships derived between various parameters and total body length. Most of the specimens found each year are fragments and head width can be used as a good predictor of total body length in each sex. Body size differs between years and between localities and male beetles show a greater degree of size inequality than females. However, L. cervus does not show greater inequality in size than many other beetle species and populations of males are composed of a relatively large number of small individuals. These males are not at a disadvantage in mating because it is the ratio of male : female size that determines mating success. Very large males are less successful in mating and it is suggested that lack of mating success may act as an additional constraint on mandible size in this species. Size variation is most likely caused by variation in larval food resources, coupled with variation in local climatic conditions. [source] Alpha male chimpanzee grooming patterns: implications for dominance "style"AMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2009M.W. Foster Abstract In social primates, individuals use various tactics to compete for dominance rank. Grooming, displays and contact aggression are common components of a male chimpanzee's dominance repertoire. The optimal combination of these behaviors is likely to differ among males with individuals exhibiting a dominance "style" that reflects their tendency to use cooperative and/or agonistic dominance tactics. Here, we examine the grooming behavior of three alpha male chimpanzees at Gombe National Park, Tanzania. We found that (1) these males differed significantly in their tendency to groom with other males; (2) each male's grooming patterns remained consistent before, during and after his tenure as alpha, and (3) the three males tended to groom with high- middle- and low-ranking partners equally. We suggest that body mass may be one possible determinant of differences in grooming behavior. The largest male exhibited the lowest overall grooming rates, whereas the smallest male spent the most time grooming others. This is probably because large males are more effective at physically intimidating subordinates. To achieve alpha status, a small male may need to compensate for reduced size by investing more time and energy in grooming, thereby ensuring coalitionary support from others. Rates of contact aggression and charging displays conformed to this prediction, suggesting that each male exhibited a different dominance "style." Am. J. Primatol. 71:136,144, 2009. © 2008 Wiley-Liss, Inc. [source] Intraguild interactions promote assortative mating and affect sexual attractiveness in a phytophagous flyBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009TOM READER Changes in acoustic and substrate-borne sexual signals in phytophagous insects associated with host plant shifts are known to have the potential to promote assortative mating, reproductive isolation and speciation. In this article, we ask whether the switch between pure herbivory and intraguild predation (IGP), which is common amongst phytophagous insects, has similar potential. Male flies in the genus Lipara (Diptera: Chloropidae) search for females by vibrating reed stems and waiting for a reply. By kleptoparasitizing other phytophagous species in the genus (a form of IGP), Lipara rufitarsis can increase its nonsexual fitness considerably. We looked at the impact of IGP on the timing of hatching, body size and attractiveness of male calls in L. rufitarsis. L. rufitarsis males that had engaged in IGP hatched significantly earlier than purely phytophagous flies and were significantly larger, but their calls were less likely to elicit responses from females during playback experiments. We conclude that, although behavioural observations of females provided no evidence of ,like preferring like', changes in phenology associated with IGP are likely to promote assortative mating in this system. The general preference of females for the calls of smaller males is a phenomenon worthy of further study: it may have no adaptive significance, or it may indicate that mating with large males is associated with a fitness cost. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 171,180. [source] Size-dependent mating strategies and the risk of cannibalismBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2008MARK A. ELGAR The role of sexual selection in determining the nature and direction of sexual size dimorphism may depend upon the timing of sexual selection, and this may also influence the variation in male size. For example, selection through sperm competition favours smaller males in the highly sexually size dimorphic orb-weaving spider Nephila edulis, whereas larger males are better able to exclude their smaller rivals from the central hub of the web where mating takes place. We investigate experimentally the role of body size and hub tenure in determining male fertilization success when males of different sizes compete for a single female over a 24-h period that includes a period of darkness. Our results confirm that small and large males obtain similar paternity share but that, in contrast with previous studies, hub tenure does not translate into greater paternity share. Unexpectedly, smaller males are at greater risk of postmating sexual cannibalism than larger males, suggesting that natural selection through sexual cannibalism may place a lower limit on male size. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 355,363. [source] | ||||||||||