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Male Bias (male + bias)
Selected AbstractsThe effect of sperm storage and timing of mating on offspring sex ratios in the yellow dung fly Scatophaga stercorariaECOLOGICAL ENTOMOLOGY, Issue 3 2000Nicola J. Seal Summary 1. Offspring sex ratios in the yellow dung fly Scatophaga stercoraria were examined in the laboratory. 2. Previous work indicated that females using previously stored sperm to fertilise their eggs produced male-biased sex ratios. This result may have been due to female influences or the effects of sperm storage per se. 3. This pattern was not reproduced in the study presented here. Females that were allowed to mate just prior to oviposition produced similarly male-biased sex ratios to those females that used previously stored sperm to fertilise their clutch. 4. Captive-reared females may have perceived a lack of males in the population and thus produced a male-biased offspring sex ratio. Alternatively, gamete ageing or extra-chromosomal sex ratio distorters may have produced the male bias. [source] Tawny Owls Strix aluco with reliable food supply produce male-biased broodsIBIS, Issue 1 2007KASI B. DESFOR Tawny Owls Strix aluco have been reported to skew the sex ratio of their offspring towards males when facing food shortage during the nestling period (and vice versa), because female fitness is more compromised by food shortage during development than male fitness. To test the generality of these results we used a DNA marker technique to determine the sex ratio in broods of Tawny Owls in Danish deciduous woodland during two years of ample food supply (rodent population outbreak) and two years of poor food supply. Of 268 nestlings, 59% were males (95% CI: 53,65%). This proportion was higher than previously reported for the species (49% in Northumberland, UK, and 52% in Hungary), but consistent with Fisherian sex allocation, which predicts a male bias of c. 57% based on inferred differences in energy requirements of male and female chicks. Contrary to previous results, brood sex ratios were not correlated with the resource abundance during the breeding seasons, despite considerable variation in breeding frequency, brood size or hatching date across years. Brood sex ratios were unaffected by brood reduction prior to DNA sampling, and nestling mortality rates after DNA sampling were not related to gender. The inconsistency between the sex ratio allocation patterns in our study and previous investigations suggests that adaptive sex allocation strategies differ across populations. These differences may relate to reproductive constraints in our population, where reproductive decisions seem primarily to concern whether to lay eggs at all, rather than adjust the sex ratio to differences in starvation risk of nestlings. [source] Sex and age influence intestinal parasite burden in three boreal grouse speciesJOURNAL OF AVIAN BIOLOGY, Issue 5 2006Marja Isomursu Parasite infections are often more common in male vertebrates than in females. Sexual selection leading to dimorphism can cause sexual differences in immune defence, behaviour or body size. Possible proximate explanations for male bias in parasitism are the immunosuppressive effect of male sex hormones and the large body size of males which increases the likelihood of being parasitized. To evaluate these hypotheses, we studied the prevalence and abundance of intestinal helminth parasites in three boreal grouse species, the capercaillie Tetrao urogallus, the black grouse Tetrao tetrix, and the hazel grouse Bonasa bonasia. The first two are sexually dimorphic polygynous species while the latter species is sexually monomorphic and monogamous. We found a male-bias in the prevalence and abundance of the nematode Ascaridia compar. The bias was most pronounced in the polygynous black grouse and capercaillie. In the monogamous hazel grouse, there was a slight male-bias in occurrence of ascarids, but no bias in abundance. In juvenile grouse, the male-bias was larger than in adult grouse. No sexual bias was found in regard to the cestodes (Skrjabinia cesticillus, Paroniella urogalli and Hymenolepis spp.). However, age was a factor in cestode prevalence: juvenile grouse were more commonly infected than adults. Differences in growth rates and body size are potential factors that may lead to male-biased parasitism in these grouse species, and their impact requires further studies. [source] Resource allocation in the red ant Myrmica ruginodis, an interplay of genetics and ecologyJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2001L. Walin Worker-queen conflicts over reproductive allocation (colony maintenance vs. reproduction) and sex allocation (females vs. males) were examined in two populations of the facultatively polygynous ant Myrmica ruginodis. Plasticity of social organization in the form of two co-existing social types (microgyna and macrogyna) has a profound effect on reproductive allocation. Workers control sex allocation by biasing sex ratios towards their own interest, but local resource competition (LRC) because of restricted dispersal of microgyna females resulted in male bias in one study population. Colony sex ratios were split and followed the predictions of the split sex ratio theory: single queen colonies with higher relatedness asymmetry (RA) produced more females than multiple queen colonies with lower RA. Single and multiple queen colonies showed similar patterns in most aspects of their reproduction, and reproductive allocation could not be explained by the hypothesis tested. This suggests that reproductive allocation conflict is of minor importance in M. ruginodis. [source] Fine-scale genetic pattern and evidence for sex-biased dispersal in the túngara frog, Physalaemus pustulosusMOLECULAR ECOLOGY, Issue 12 2003Kathrin P. Lampert Abstract Túngara frogs (Physalaemus pustulosus) are a model system for sexual selection and communication. Population dynamics and gene flow are of major interest in this species because they influence speciation processes and microevolution, and could consequently provide a deeper understanding of the evolutionary processes involved in mate recognition. Although earlier studies have documented genetic variation across the species' range, attempts to investigate dispersal on a local level have been limited to mark,recapture studies. These behavioural studies indicated high mobility at a scale of several hundred metres. In this study we used seven highly polymorphic microsatellite loci to investigate fine-scaled genetic variation in the túngara frog. We analysed the influence of geographical distance on observed genetic patterns, examined the influence of a river on gene flow, and tested for sex-biased dispersal. Data for 668 individuals from 17 populations ranging in distance from 0.26 to 11.8 km revealed significant levels of genetic differentiation among populations. Genetic differentiation was significantly correlated with geographic distance. A river acted as an efficient barrier to gene flow. Several tests of sex-biased dispersal were conducted. Most of them showed no difference between the sexes, but variance of Assignment Indices exhibited a statistically significant male bias in dispersal. [source] Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus)MOLECULAR ECOLOGY, Issue 7 2001D. J. Girman Abstract African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal. [source] Sex Ratio of Some Long-Lived Dioecious Plants in a Sand Dune AreaPLANT BIOLOGY, Issue 5 2004T. J. de Jong Abstract: In dioecious plants the fraction of males among flowering plants in the field (the secondary sex ratio) is the result of the fraction of males in the seeds (the primary sex ratio) and the subsequent survival and age at first reproduction of the two genders. It has been assumed that survival and age at first reproduction are the main determinants of biased secondary sex ratio but, especially for long-lived perennials, few data are available. We address this issue for natural populations of four long-lived perennials in a dune area. In Asparagus officinale and Bryonia dioica, the secondary sex ratio was unbiased. In Salix repens the secondary sex ratio was female-biased (0.337). Hippophae rhamnoides populations were male-biased; the average sex ratio of flowering plants was 0.658, while the fraction of males varied between 0.39 near the sea to 0.84 at the inland side of the dunes. The primary sex ratio was estimated by germinating seeds and growing plants under favourable conditions with minimal mortality. In S. repens the primary sex ratio in seeds was variable among mother plants and was, on average, female-biased (0.289). This is close to the secondary sex ratio, suggesting that the female bias already originates in the seed stage. In Hippophae rhamnoides the primary sex ratio was slightly male-biased (0.564). We argue that in this species, apart from the primary sex ratio, higher mortality and a later age at first reproduction for females contribute to the strong male bias among flowering plants in the field. [source] Demographic monitoring of an entire species (the northern hairy-nosed wombat, Lasiorhinus krefftii) by genetic analysis of non-invasively collected materialANIMAL CONSERVATION, Issue 2 2003Sam C. Banks Successful management of endangered species may be greatly facilitated by the ability to monitor population trends. The Australian northern hairy-nosed wombat (Lasiorhinus krefftii) is one of the world's most endangered mammals, but precise abundance estimation by trapping surveys has proven exceedingly difficult. A mark-recapture study was conducted in the sole remaining L. krefftii population, based on microsatellite identification of individuals and their gender from DNA in remotely collected single hairs. Population size was estimated to be 113 (95% confidence interval of 96 to 150). This suggests an increase in population size over the previous estimate of 65 (95% CI 42,186) in 1993, although the estimates did not differ significantly. There was a significant male bias in the sex ratio (2.25 males:1 female), in agreement with recent trapping surveys. The non-invasive approach used here is vital for estimating population size and trends, and hence it is the most important recent advance in the conservation management of the northern hairy-nosed wombat. [source] Gorgonian population recovery after a mass mortality eventAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2005C. Cerrano Abstract 1.Mass mortality events are becoming more common all over the world, both in tropical and temperate seas. An extensive mortality occurred in the Mediterranean Sea in 1999, affecting many benthic species, mainly sponges and gorgonians. 2.The recovery of a population of the sea fan Paramuricea clavata, for a period of 3 yr, from 1999 to 2002, was studied by both line transects and fixed frames. The average size of the colonies decreased, indicating a size-dependent mortality episode, but their density, as a result of successful recruitment, was not altered after 3 yr. 3.P. clavata showed three recovery patterns: (i) sexual reproduction, (ii) coenenchyme regeneration and (iii) fragmentation of affected branches. Moreover, the growth rates of small colonies varied in the different years. The sex ratio of the population was also altered, with females being more affected than males; the population studied showed a significant male bias (3.3:1, n=150), varying greatly from the typical sex ratio (1:1) previously recorded in the same population before the mass mortality event. Copyright © 2004 John Wiley & Sons, Ltd. [source] The evolution of male mate choice in insects: a synthesis of ideas and evidenceBIOLOGICAL REVIEWS, Issue 3 2001RUSSELL BONDURIANSKY ABSTRACT Mate choice by males has been recognized at least since Darwin's time, but its phylogenetic distribution and effect on the evolution of female phenotypes remain poorly known. Moreover, the relative importance of factors thought to underlie the evolution of male mate choice (especially parental investment and mate quality variance) is still unresolved. Here I synthesize the empirical evidence and theory pertaining to the evolution of male mate choice and sex role reversal in insects, and examine the potential for male mating p to generate sexual selection on female phenotypes. Although male mate choice has received relatively little empirical study, the available evidence suggests that it is widespread among insects (and other animals). In addition to ,precopulatory' male mate choice, some insects exhibit ,cryptic' male mate choice, varying the amount of resources allocated to mating on the basis of female mate quality. As predicted by theory, the most commonly observed male mating p are those that tend to maximize a male's expected fertilization success from each mating. Such p tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity. Among insect species there is wide variation in mechanisms used by males to assess female mate quality, some of which (e.g. probing, antennating or repeatedly mounting the female) may be difficult to distinguish from copulatory courtship. According to theory, selection for male choosiness is an increasing function of mate quality variance and those reproductive costs that reduce, with each mating, the number of subsequent matings that a male can perform (,mating investment'). Conversely, choosiness is constrained by the costs of mate search and assessment, in combination with the accuracy of assessment of potential mates and of the distribution of mate qualities. Stronger selection for male choosiness may also be expected in systems where female fitness increases with each copulation than in systems where female fitness peaks at a small number of matings. This theoretical framework is consistent with most of the empirical evidence. Furthermore, a variety of observed male mating p have the potential to exert sexual selection on female phenotypes. However, because male insects typically choose females based on phenotypic indicators of fecundity such as body size, and these are usually amenable to direct visual or tactile assessment, male mate choice often tends to reinforce stronger vectors of fecundity or viability selection, and seldom results in the evolution of female display traits. Research on orthopterans has shown that complete sex role reversal (i.e. males choosy, females competitive) can occur when male parental investment limits female fecundity and reduces the potential rate of reproduction of males sufficiently to produce a female-biased operational sex ratio. By contrast, many systems exhibiting partial sex role reversal (i.e. males choosy and competitive) are not associated with elevated levels of male parental investment, reduced male reproductive rates, or reduced male bias in the operational sex ratio. Instead, large female mate quality variance resulting from factors such as strong last-male sperm precedence or large variance in female fecundity may select for both male choosiness and competitiveness in such systems. Thus, partial and complete sex role reversal do not merely represent different points along a continuum of increasing male parental investment, but may evolve via different evolutionary pathways. [source] | ||||||||||||||||||||||