Extra-pair paternity in the monogamous alpine marmot (Marmota marmota): the roles of social setting and female mate choice

Extra-pair paternity (EPP) can be influenced by both social setting and female mate choice. If evidence suggests that females try to obtain extra-pair copulations (EPCs) in order to gain genetic benefits when mated to a homozygous and/or to a related male, females may not be able to choose freely among extra-pair mates (EPMs) as the social mate may constrain female access to EPMs. In this study, we investigated, first, how EPP depended on social setting and specifically on the number of subordinate males in the family group in a highly social and monogamous mammal, the alpine marmot. Second, we investigated how EPP depended on female mate choice for genetic benefits measured as male mate-heterozygosity and within-pair relatedness. Our results reveal, first, that EPP depended on the social setting, increasing with the number of subordinate males. Second, EPPs were related to relatedness between mates. Third, EPMs were found to be more heterozygous than within-pair males. Thus, social setting may constrain female choice by limiting opportunities for EPC. However, after accounting for social confounding factors, female choice for genetic benefits may be a mechanism driving EPP in monogamous species.     

Oviposition site guarding by male walnut flies and its possible consequences for mating success

Field studies showed that male Rhagoletis juglandis and R. boycei flies guard egg-laying punctures (and the eggs within) on host walnut (Juglans major) fruit and defend those sites from conspecific and heterospecific males. In field experiments with artificially punctured fruit,as well as field observations on unmanipulated fruit, males were consistently more likely to be sighted and stayed longer on damaged fruit than on undamaged fruit. On artificially punctured fruit, they consistently spent more time in the vicinity of a puncture than expected by chance alone. Males together on damaged fruit were more likely to engage in contests over those fruit than males together on undamaged fruit. Copulations were consistently more frequent for either species on damaged than undamaged fruit, both in observations of unmanipulated fruit and in artificial puncture experiments. Analyses which controlled for the longer male residence time on damaged fruit suggested strongly that copulations were consistently achieved at higher per capita rates on damaged than on undamaged fruit, indicating that puncture-guarding functions to increase access to females. An exception to the pattern in male mating success was noted at a site where both species used host fruit on the same trees. In this case, R. juglandis males were only slightly more common on punctured fruit than on control fruit and male success in copulation did not differ significantly between the two types of fruit. This anomalous result was apparently due to an almost absolute advantage enjoyed by R. boycei males in on-fruit contests with R. juglandis males. A likely basis for improvements in mating success associated with puncture guarding was a propensity for females to deposit eggs into existing punctures. Both in observations of unmanipulated fruit and in artificial puncture experiments, females consistently attempted oviposition more often in damaged than undamaged fruit. In artificial puncture experiments, both species at both sites deposited most clutches in damaged fruit. Mating generally took place as females initiated oviposition. The possible functions of puncture use by females as well as alternative functions of puncture guarding by males are discussed.     

Intrasexual selection in Mirza coquereli : evidence for scramble competition polygyny in a solitary primate

The primates of Madagascar (Lemuriformes) deviate from fundamental predictions of sexual selection theory in that polygynous species lack sexual dimorphism, have even adult sex ratios and often live in female-dominated societies. It has been hypothesized that intrasexual selection in these species is either reduced or primarily focused on traits related to scramble competition. The goal of this study was to examine these hypotheses by studying the mating system of a solitary nocturnal species, Mirzacoquereli. During a 4-year field study in western Madagascar, I captured and followed 88 individually marked animals. I found that adult males were significantly larger than females, providing the first evidence for sexual size dimorphism in lemurs. In addition, the adult sex ratio was biased in favour of females in 3 out of 4 years. There was no significant sex difference in canine size, however. Males showed pronounced seasonal variation in testis size with a 5-fold increase before and during the short annual mating season. During the mating season, males had more injuries than females and more than quadrupled their home ranges, overlapping with those of more than ten females, but also with about the same number of rivals. Only about one social interaction per 10 h of observation was recorded, but none of them were matings. Together, these results indicate that these solitary lemurs are clearly subject to intrasexual selection and that male-male competition is primarily, but not exclusively, of the scramble type. In addition, they suggest that the above-mentioned idiosyncracies may be limited to group-living lemurs, that social systems of solitary primates are more diverse than previously thought, and that the temporal distribution of receptive females is responsible for this particular male mating strategy. Received: 11 January 1997 / Accepted after revision: 18 April 1997     

四川农业资源开发利用与保护对策

农业资源系指农业自然资源和农村经济社会资源的总称。本文试从四川农业资源的特点和开发利用与保护存在的问题,探索农业资源开发与保护的策略。     

Sexual cannibalism facilitates genital damage in <Emphasis Type="Italic">Argiope lobata</Emphasis> (Araneae: Araneidae)

Sperm competition is a potent driving force in evolution leading to a remarkable variety of male adaptations that prevent or reduce fertilization by rivals. An extraordinary defensive strategy against sperm competition has evolved in a number of web spiders where males break off parts of their paired genitalia in order to obstruct the copulatory openings of females (mating plug). A recent comparative analysis on the family level reports that genital damage is most frequent in species with sexual cannibalism although, as yet, a functional association between sexual cannibalism and genital damage has not been found. Using the moderately sexually cannibalistic orb-web spider Argiope lobata, we show for the first time that males cannibalized during their first copulation damaged their pedipalps with significantly higher probability (74%) than males that escaped (15%). Of all males that damaged their genitalia, 44% were able to place a genital fragment inside the copulatory opening of the female, resulting in a relatively low total plugging rate of 14%. Successful obstruction of the female copulatory opening reduced the share of paternity of subsequent males (P ₂ = 0.06%), thus, indicating that genital damage may have evolved as a response to sperm competition in this species as well. However, the low incidence of successful plugging and the strong relationship between sexual cannibalism and genital damage suggest that apart from paternity protection, the nature of genital damage in A. lobata is further shaped by sexual conflict or cryptic female choice.     

Effects of mating history on ejaculate size, fecundity, longevity, and copulation duration in the ant-tended lycaenid butterfly, Jalmenus evagoras

The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an ’explosive mating strategy,’ include the formation of an intensely competitive mating aggregation of males, a highly male biased operational sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy. In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores, and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second mating and the dry weight by 29%, and an intermating interval of 5–9 days was needed for the ejaculate to return to the size at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number. Received: 22 January 1999 / Received in revised form: 28 July 1999 / Accepted: 18 September 1999     

Effect of sperm depletion and starvation on female mating behavior in the water strider,Aquarius remigis

The resolution of intersexual conflict over mating should be dependent on the current state of each individual. In this study, I used a factorial design to examine the influence of two physiological factors, sperm depletion and food deprivation, on resistance to mating by females of the water strider, Aquarius remigis. Females employ several different mate-resisting tactics during an encounter with a male. Five measures of female resistance to mating were identified: jumping, rolling, dunking, time spent dunking, and struggle duration. Jump, roll, and dunk rates were highly correlated with each other and combined into one metric of resistance to mating (PC1) using principal components analysis. Time per dunk (T/D) and struggle duration were also analyzed. Discrete male behaviors during the struggle could not be identified. Two measures of female resistance, PC1 and T/D, were significantly lower in sperm-depleted females than in sperm-replenished females. Struggle duration did not differ between the two treatments. Starvation had no effect on any of the measures of resistance. Sperm depletion significantly enhanced the probability of mating (54% vs. 24% for replenished females), while starvation had no effect on the probability of mating. I pooled all the females and compared females that mated with those that did not mate. Nonmating females resisted significantly more than mating females in all three measures of resistance. Path analysis indicated that PC1 was the only measure of resistance that was significantly negatively related to the probability of mating. Almost half (46%) of sperm-depleted females showed no resistance to males, while only 3% of sperm-replenished females were nonresistant. When nonresisters were removed from the analysis, sperm depletion had no effect on any of the measures of female resistance to mating and no effect on the probability of mating. In A. remigis, female resistance appears to be a yes/no phenomenon with respect to sperm depletion and not affected directly by starvation. Received: 2 September 1994/Accepted after revision: 9 September 1995     

Egg mimicry and allopaternal care: two mate-attracting tactics by which nesting striped darter (Etheostoma virgatum) males enhance reproductive success

In a variety of fish species with paternal care of offspring, females prefer to spawn in nests that already contain eggs. This female preference has been hypothesized to explain egg thievery in male sticklebacks, allopaternal care of eggs in minnows, and the evolution of egg-mimicking body features in male cichlids and darters. Here we employ microsatellite-based parentage analyses to evaluate the reproductive success of striped darter (Etheostoma virgatum) males that appear to utilize two of these functionally related tactics to entice females to spawn in their nests. In an isolated population (Clear Creek, Ky.), we observed that breeding males develop conspicuous white spots on their pectoral fins. If these spots are egg mimics, as we suspect, then this represents the fourth independent evolutionary origin of egg mimicry documented to date in darters, the first based on pigmentation (as opposed to physical structures), and the first in which the egg mimics vary greatly in number among males. From direct counts of microsatellite genotypes in clutches of embryos, at least 3.8 females contributed to the progeny within a typical nest, and females tended to spawn preferentially with males that were larger and displayed more egg-mimic spots. In another population (Hurricane Creek, Tenn.) without egg mimics, the multi-locus genetic data document that allopaternal care is common, especially among the smallest males who sometimes tend nests containing their own as well as an earlier sire's offspring. Thus, these foster males had adopted egg-containing nests and then successfully spawned with subsequent females. Overall, the genetic data on paternity and maternity, in conjunction with field observations, suggest that egg mimicry and allopaternal care are two mate-attracting reproductive tactics employed by striped darter males to exploit female preferences for spawning in nests with 'eggs'. Electronic Publication     

Sexual contact influences orientation to plant attractant in Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)

Chemical signals emitted by insects and their hosts are important for sexual communication and host selection. Plant volatiles facilitate the location of suitable hosts for feeding and oviposition, and may moderate responses to sex and aggregation pheromones. While mating has been shown to moderate behavioral responses to pheromones in a number of insects, little is known about the effects of mating on behavioral responses of insects to plant attractants, and even less is known about the mechanisms involved. In this study, mating was shown to decrease behavioral responses of the Colorado potato beetle to a host kairomone within 24 h, and attraction to the kairomone recovers only after 72 h. This decrease in responsiveness also occurs when only contact with the opposite sex is allowed; the effect is not observed with contact among individuals of the same sex. Peripheral olfactory responses to a component of the kairomone correlate with the observed behavioral responses and suggest involvement of antennal receptors in the behavioral change.     

Variation in homeward orientation performance in the sleepy lizard (Tiliqua rugosa): effects of sex and reproductive period

Sleepy lizards are monogamous skinks which show high pair fidelity. This study reveals inter- and intrasexual differences in homeward orientation performance in this lizard. Male and female lizards were displaced during three phases of the spring activity period, the pre-pairing, pairing/mating, and post-pairing periods. All groups (with the exception of post-pairing males) were significantly oriented homewards, but males were significantly better oriented towards home than females during the pairing period. Furthermore, males were significantly better homeward oriented during the pre-pairing and pairing periods than in the post-pairing period. Similar results were observed for rate of movement away from the release site. In sleepy lizards, sex-based differences in homing behaviour are unlikely to be attributable to differences in the area of familiarity, or availability of orientation mechanisms. However differences in homing motivation may explain these differences. Males may miss mating if absent from the home range during the pre-pairing and pairing periods, while females may still be able to obtain a mating even when absent. Females however may be more motivated than males to return to the familiar home range during the post-pairing period to ensure efficient feeding during internal embryo development. Received: 16 February 1998 / Accepted after revision: 28 March 1998