Spatial organization and mating system of Microtus townsendii

Summary Space use by individual Townsend's voles, Microtus townsendii, was investigated in spring and summer by means of radiotelemetry and intensive live trapping in undisturbed grasslands near Vancouver, British Columbia. Home ranges of males were larger than those of females; females had significantly larger ranges in spring than in summer. Most males and females maintained territories free of individuals of the same sex in spring. Male-female pairs had their exclusive territories closely overlapping each other. The 1:1 operational sex ratio and the spatial association of pairs of males and females suggest that the voles were monogamous in the spring of 1988 and that 50% of the males were monogamous in the spring of 1989. In summer, there was more intrasexual overlap between home ranges of males and females and female ranges were considerably smaller than those of males. Females were more philopatric than males and females thought to be members of the same family group lived adjacent to each other or had overlapping home ranges. Males overlapped with more than one female in summer, but most females still overlapped with only one male, which suggests that the mating system is polygynous in summer. Thirty-five percent of the philopatric females became pregnant for the first time when the male spatially associated with their mother in the spring was still alive and thus could potentially have mated with their fathers. Male and female territoriality in spring is the proximate mechanism for the limitation of breeding density by spacing behaviour.[/p] Offprint requests to: C.J. Krebs     

Costs of courtship and mating in a sexually cannibalistic orb-web spider: female mating strategies and their consequences for males

The costs of courtship and mating may include increased risks of predation, the transmission of pathogens, and a loss of foraging opportunities. Thus, a female's decision to tolerate a courting male will depend upon how these costs offset the benefits of mating, which will depend on her reproductive and nutritional status. While these costs may be similar for mated and unmated females, the benefits of mating will be less for mated than virgin females. However, the cost of lost foraging opportunities may be higher for females with fewer nutritional reserves necessary for forming eggs. We examined how these costs and benefits influence the courtship and mating behaviour of male and female orb-web spiders, Argiope keyserlingi. In the field, females on webs that also contained a courting male intercepted fewer prey items per hour than females on webs without a male. In the laboratory, the presence of a courting male at the hub also attracted mantid predators to the web, increasing the risk of predation for both male and female. Staged mating experiments in the laboratory revealed that the frequency of female attacks and pre-copulatory cannibalism was greater among mated than virgin females. Feeding history did not affect aggression in virgin females but, among mated females, food-deprived spiders attacked and cannibalized males more frequently than sated females and only the latter ever remated. These differences in female behaviour influenced male mating strategies. Choice experiments demonstrated that males preferred to venture onto the silk threads of virgin rather than those of mated females. Similar patterns of mate selectivity were observed in the field; females with narrow abdomens attracted more males to the webs than females with broad abdomens, and copulations were observed more frequently among females with narrow abdomens. These smaller females are likely to be virgins that have recently molted. Males that preferentially mate with virgin females will not only avoid potentially fatal attacks but also obtain, on average, a higher fertilization success.     

Alternative mating strategies in the water strider Gerris elongatus (Heteroptera,Gerridae)

Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution.     

A comparative analysis of sperm storage and mating strategies in five species of brachyuran crabs

Variation in female sperm storage is explained, in part, by the amount of sperm transferred at mating. Laboratory mating experiments were conducted on Eurypanopeus depressus and Rhithropanopeus harrisii from the Chesapeake Bay and Pachygrapsus transversus from Florida, while mated pairs of Uca beebei and U. terpsichores were collected from mudflats in Panama. All experiments and collections were conducted during the summer of 2006 and 2007. More sperm was transferred to larger than smaller females, and by species with long copulation durations (R. harrisii and E. depressus). These two species live in cryptic habitats, have high sperm/egg ratios, and likely store sperm across multiple broods. In contrast, P. transversus and U. beebei mate conspicuously, have short copulations, transfer fewer sperm, and have low sperm/egg ratios. Comparisons of sperm transfer across different mating strategies and habitats provide a better understanding of female sperm storage in the Brachyura.     

Lek structure and territoriality in the chryxus arctic butterfly,Oeneis chryxus (Satyridae)

Summary The territorial and mating systems of the satyrid butterfly Oeneis chryxus were studied for 3 years on individually marked populations in algonquin Provincial Park, Ontario. Males defended territories in a dry open forest clearing by means of chases and spiral flights with conspecifies. Defended areas did not contain food or oviposition sites required by females. Territories were not uniformly distributed over the study area; the highest density of territories was clustered over bare ground covered with sand and small stones rather than areas of vegetation. This pattern of distribution of territories occurred during each year of the study. The patterns of occupancy of territories showed a high degree of consistency from one day to the next, some males defending a given territory for as many as 11 consecutive days. Removal experiments showed that a surplus of non-territorial males did not exist. Vacant territories in the high-density area were absorbed by neighboring males; those in the low-density area remained empty. Male size was not correlated with territory position in the study are. Wing patterning (i.e. size of spots) differed between males occupying territories on sandy/stony versus vegetated areas. The territorial and mating systems of O. chryxus resemble lek polygyny, and are more similar to some vertebrate lek systems than to hilltopping or landmark territoriality.     

Mating strategies and mating success of fallow (Dama dama) bucks in a non-lekking population

The rutting behaviour of bucks in an enclosed population was investigated between 1988 and 1990. A substantial proportion of the matings were observed. After preliminary observations in the 1987 rut we categorised bucks into one of four rutting strategies based mainly on their degree of territoriality. We investigate the effects of age, dominance and mating strategy on mating success. Territories were aggregated in an area of oak woods and mating success was highly skewed. Bucks of between 5 and 7 years old achieved the majority (over 90%) of observed matings. Mating success was highly correlated with dominance but only weakly related to fighting success. The possession of a territory was crucial to achieving high reproductive success, with a 38-fold difference between the most and least successful strategies. Bucks pursuing the different strategies also differed in the time they commenced groaning, timing of matings, mating interference and the locations where they achieved their matings. Although high-ranking males devoted considerable effort to obtaining and defending a territory only 36% of each buck's matings were achieved on his territory and males tended to abandon these sites when the tendency of females to visit them decreased.     

Large males dominate: ecology,social organization,and mating system of wild cavies,the ancestors of the guinea pig

Ecological factors differently affect male and female animals and thereby importantly influence their life history and reproductive strategies. Caviomorph rodents are found in a wide range of habitats in South America and different social and mating systems have evolved in closely related species. This permits to study the impact of ecological factors on social evolution. In this study, we investigated the social organization and the mating system of the wild cavy (Cavia aperea), the ancestor of the domestic guinea pig, in its natural habitat in Uruguay. Based on our laboratory investigations, we expected a polygynous system with large males controlling access to females. Results from radiotelemetry and direct observations showed that females occupied small stable home ranges which were largely overlapped by that of one large male, resulting in a social organization of small harems. In some cases, small satellite males were associated with harems and intermediate-sized roaming males were occasionally observed on the study site. However, microsatellite analyses revealed that offspring were exclusively sired by large males of the same or neighboring harems, with a moderate degree of multiple paternity (13–27%). Thus, the mating system of C. aperea can be described as polygynous and contrasts with the promiscuous organization described for other species of cavies (Cavia magna, Galea musteloides and Microcavia australis) living under different ecological conditions. Our findings stress the strong impact of environmental factors on social evolution in Caviomorphs as resource distribution determines female space use and, thereby, the ability of males to monopolize females. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Divorce and extrapair mating in female black-capped chickadees (Parus atricapillus): separate strategies with a common target

Patterns of divorce and extrapair mating can provide insights into the targets of female choice in free-living birds. In resident, site-faithful species with continuous partnerships, the better options and the incompatibility hypotheses provide the most likely explanations for divorce. Extrapair mating can be explained by a number of hypotheses often making similar predictions. For example, the good genes and future partnerships hypo- theses predict similar patterns if males with good genes also make the best future partners. By considering both divorce and extrapair mating, it may be possible to distinguish between these comparable hypotheses. We examined natural patterns of divorce and extrapair mating in a long-term study of black-capped chickadees (Parus atricapillus). Out of 144 partnerships over 8 years, we observed 11 divorces and 38 faithful pairs between seasons. Females usually divorced between their first and second breeding seasons for males of higher social rank than their previous partners, had similar reproductive success prior to divorce as females who retained their previous partners, and did not divorce on the basis of previous reproductive success. These results confirm earlier experimental evidence that females divorce for better options. Females who divorced were significantly more likely to have had mixed-paternity broods prior to divorce than females who stayed with their previous partners. There was no evidence that females divorced in favour of previous extrapair partners. These results support the good genes hypothesis for extrapair mating, suggesting that female chickadees use divorce and multiple mating as separate strategies sharing a common target. Received: 4 February 2000 / Revised: 20 July 2000 / Accepted: 4 September 2000     

Environmental and genetic influences on mating strategies along a replicated food availability gradient in guppies (Poecilia reticulata)

Food availability is expected to influence the relative cost of different mating tactics, but little attention has been paid to this potential source of adaptive geographic variation in behavior. Associations between the frequency of different mating tactics and resource availability could arise because tactic use responds directly to food intake (phenotypic plasticity), because populations exposed to different average levels of food availability have diverged genetically in tactic use, or both. Different populations of guppies (Poecilia reticulata) in Trinidad experience different average levels of food availability. We combined field observations with laboratory “common garden” and diet experiments to examine how this environmental gradient has influenced the evolution of male mating tactics. Three independent components of variation in male behavior were found in the field: courtship versus foraging, dominance interactions, and interference competition versus searching for mates. Compared with low-food-availability sites, males at high-food-availability sites devoted more effort to interference competition. This difference disappeared in the common garden experiment, which suggests that it was caused by phenotypic plasticity and not genetic divergence. In the diet experiment, interference competition was more frequent and intense among males raised on the greater of two food levels, but this was only true for fish descended from sites with low food availability. Thus, the association between interference competition and food availability in the field can be attributed to a genetically variable norm of reaction. Genetically variable norms of reaction with respect to food intake were found for the other two behavioral components as well and are discussed in relation to the patterns observed in the field. Our results indicate that food availability gradients are an important, albeit complex, source of geographic variation in male mating strategies.     

Repeatable female preferences, mating order and mating success in the poeciliid fish, Heterandria formosa

Sexual selection via female choice can afford preferred males comparably higher mating success than those males that lack preferred traits. In addition, many models of sexual selection assume that both male traits and female preferences are heritable. In this study we test whether females of the poeciliid fish, Heterandria formosa, have repeatable pre-copulatory preferences for larger males. We also test whether female pre-copulatory preferences are always reliable indicators of male mating success. When given a choice between a large and a small male, females prefer larger males, and the repeatability of this preference is high. Although there are no overall differences in male mating success between large and small males, large males have a higher mating success when they are the first to mate than when they are the second to mate. Likewise, preferred males also have higher mating success when they are the first to mate than when they mate second. Therefore, the repeatable female preferences observed in this study only predict male mating success when the preferred male mates first. These results illustrate that even significantly repeatable female preferences do not translate into male mating success, which is an assumption of many examinations of the importance of female choice in sexual selection.     

Availability of receptive females at the mating place and mating chances of males in the dragonfly Aeschna cyanea

Summary The females of the dragonfly Aeschna cyanea visiting ponds vary in their receptiveness to males waiting there. Individual males pay several short visits to a mating place in the course of a day, searching for receptive females. Non-receptive females prefer to oviposit at the pond in the evening, whereas receptive females arrive throughout the day. The highest number of receptive females is found on warm days during the afternoon at which time the greatest number of copulations occur. However, as the number of males and, therefore, the competition between males is also highest during these periods, the mating chances of a particular male are constant throughout the day.     

Male genital length and mating status differentially affect mating behaviour in an earwig

Phenotypic variation in male genitalia may affect copulation behaviour, which can have important fitness consequences for males. Male genitalia commonly possess traits that increase male control over copulation, but in species where females control mating, a poor functional understanding often prevents insight into the processes responsible for such effects. Here, I investigate the effect of male genital length on copulation behaviour in the earwig Euborellia brunneri, where both sexes exhibit extremely elongated genitalia that correspond in shape. This model system is particularly suitable because pairs mate repeatedly and females can limit both the number and duration of copulations. I used both virgin and mated males and females in a double-mating design because longer male genitalia confer benefits in sperm competition. Consistent with a greater predicted male mating effort in mated females, the duration of individual copulations increased, but this traded off against mating frequency as cumulative mating duration remained unchanged. In contrast, male genital length increased both individual and cumulative mating duration, regardless of mating status. This difference suggests that, while males may modify copulation duration in response to mating status, females facultatively adjust mating frequency to prevent mating excessively or express preferences for increased male genital length. Notably, this study demonstrates that male genital phenotypes that are successful in sperm competition also enjoy female-mediated mating benefits.     

Male size,mating success,and mating strategy in the mosquitofish Gambusia affinis (Poeciliidae)

Summary In laboratory choice experiments, receptive female western mosquitofish Gambusia affinis affinis (deprived of contact with males 30 days) preferred the larger of two males. When two males differing in size were placed with a receptive female, the larger was generally able to monopolize access to her, but not when the female was not receptive. In other experiments, a single male was placed with a receptive or non-receptive female. These experiments showed size-correlated differences in male mating behavior. Smaller males were more likely to chase non-receptive females and attempt to inseminate them forcibly, while larger males continued to court females even if they were non-receptive. Even when the female was receptive, there was some evidence of size-correlated differences in levels of courtship and chasing.     

Lek promiscuity in a semelparous mammal,Antechinus stuartii (Marsupialia: Dasyuridae)?

Summary All male Antechinus stuartii die following a brief rut towards the end of their first year of life. Outside the rutting period, both males and females forage in clearly-defined invidual home ranges, but neither sex is territorial. As temperatures drop during the winter, both sexes may leave their foraging range each day to spend the latter part of the night and most of the daylight hours in communal nests which may be used by fifteen animals simultaneously, and over forty individuals during one winter. These temporary movements away from the foraging range cause an increase in the daily home range revealed by radiotelemetry. When the mating season commences, males abandon their foraging range and aggregate in a few of the communal nest trees, where they spend most of the night. There is some movement between aggregations, but the movement appears to be rapid and direct. Females continue to use their foraging area, and nest solitarily. However, they make excursions to the male aggregations, and spend time in the nests with the males. By the third week of the mating season, immediately prior to male mortality, males move frequently from one aggregation to another, but are still confined to the aggregations and direct movements between those nests. By this time some females have ceased visiting the aggregations and nest solitarily within their foraging range. These data suggest that the mating system of A. stuartii is lek promiscuity, and support the hypothesis that the abrupt mortality of males is a cost of endocrine changes which facilitate gluconeogenic mobilisation of body protein, allowing the males to sustain their vigil at the leks.     

Multiple mating and the evolution of social behavior in the hymenoptera

Summary The data on the frequency of mating by queens of eusocial Hymenoptera are reviewed.It is pointed out that the issue of sperm clumping is probably irrelevant to the evolution of eusociality.The hypothesis is presented that multiple mating is an adaptation for maintaining large colonies. In ants there is a significant relation between the size of the colony and the frequency of mating.The effect of multiple mating on the spread of a gene for worker behavior is explored. If a female mates twice, the effective number of matings is less than two except in the case of identical sperm contribution by the males.Sperm bias is defined as the contribution of unequal amounts of sperm by the males that mate with a queen. Sperm bias can be produced as a sampling phenomenon, by inter-male competition for females and by sperm competition.The relation between the ergonomic efficiency of the workers at the production of reproductives and the number of matings that is consistent with the evolution of eusociality is derived. If workers are only about 10% more efficient at producing reproductives within a eusocial colony than they are solitarily, then two matings by the queen will still produce a selective advantage to eusocial behavior.