RETRACTED: WHAT DETERMINES SEX ROLES IN MATE SEARCHING?

In a seminal paper, Hammerstein and Parker (1987) described how sex roles in mate searching can be frequency dependent: the need for one sex to perform mate searching is diminished when the opposite sex takes on the greater searching effort. Intriguingly, this predicts that females are just as likely to search as males, despite a higher potential reproductive rate by the latter sex. This prediction, however, is not supported by data: male mate searching prevails in nature. Counterexamples also exist in the empirical literature. Depending on the taxon studied, female mate searching can arise in either low- or high-density conditions, and suggested explanations differ accordingly. We examine these puzzling observations by building two models (with and without sperm competition). When sperm competition is explicitly included, male mate searching becomes the dominant pattern; when it is excluded, male mate searching predominates only if we assume that costs of searching are higher for females. Consequently, two hypotheses emerge from our models. The multiple-mating hypothesis explains male searching on the basis of the ubiquity of sperm competition, and predicts that female searching can arise in low-density situations in which sperm can become limiting. It can also explain cases of female pheromone production, where males pay the majority of search costs. The sex-specific cost hypothesis predicts the opposite pattern of female searching in high-density conditions, and it potentially applies to some species in which sperm limitation is unlikely.     

Sperm Storage and Use After Multiple Mating in Dinarmus basalis (Hymenoptera: Pteromalidae)

Multiple mating and its effects on the sex ratio in Dinarmus basalis (Hymenoptera: Chalcidoidea, Pteromalidae), an ectoparasitoid of Callosobruchus maculatus (Coleoptera: Bruchidae), were investigated under controlled conditions. Once-mated females suffer a sperm depletion about 21 days after mating and thereafter are constrained to produce only haploid males. On the other hand, three-times-mated females store more sperm in their spermathecae (335 vs 147) and produce daughters during the major part of their reproductive life. Consequently, once-mated females showed a male-biased life time sex ratio (mean = 0.31) as opposed to three-times-mated females (mean = 0.63). Females can copulate only at the beginning of their reproductive life, and multiple mating must occur before egg-laying activity. This behavioral strategy could be an avoidance of consanguinity in a promiscuous environment. This ectoparasitoid species reveals a reproductive strategy which promotes polyandry and a very high sperm efficiency.     

The effect of sperm storage and timing of mating on offspring sex ratios in the yellow dung fly Scatophaga stercoraria

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.     

Effects of age and repeated mating on male sperm supply and paternity in a parasitoid wasp

Post-copulatory paternity biases after female multiple mating are major constraints on both male and female reproductive systems. The outcome of paternity in certain situations is only controlled directly by male sperm stock. This was tested experimentally in the parasitoid wasp Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), in which sperm stocks are small (several hundred) and the fertilizing efficiency of stored sperm is high (the ratio of sperm stored/fertilized eggs is about 0.75). Sperm in seminal vesicles and paternity of males of different status (virgin young, virgin old, or young previously mated) were measured after female single and double mating. The amount of sperm in the seminal vesicle differed according to male status (increasing from previously mated males to old males), but there was no difference in sperm stored by females after a single mating. In double mating experiments with two males of different status, paternity increased linearly with the relative amount of sperm in seminal vesicles. Paternity distribution conforms to 'a fair raffle' of sperm from both donors following complete mixing of sperm prior to fertilization. Thus, in a female multiple mating context, male fitness depends principally on their sperm stock, which in turn depends on life history parameters, such as age and previous mating.     

Spontaneous male death and monogyny in the dark fishing spider

Monogyny (male monogamy) is found in a diverse assemblage of taxa, and recent theoretical work reveals that a male-biased sex ratio can favour the evolution of this relatively rare mating system. We integrate this theoretical framework with field observations and laboratory experiments involving the sexually size dimorphic fishing spider, Dolomedes tenebrosus, to test the prediction that this species exhibits monogyny. Field surveys revealed a male-biased sex ratio, likely resulting from different life-history strategies (early male maturation). Results from mating trials supported our prediction of monogyny as we discovered that males mate with a single female. Unexpectedly, however, we observed that mating results in obligate male death and genital mutilation. Additional field observations of released individuals suggest that males are not limited by their ability to encounter additional females. Controlled laboratory assays demonstrated that males discriminate among virgin and non-virgin female silk cues, consistent with predictions of first-male sperm precedence. In summary, we report a novel case of male self-sacrifice in a species that exhibits female-biased sexual size dimorphism, male-biased sex ratio, genital mutilation and a suggestion of first-male sperm precedence; all of which are consistent with theoretical predictions of the evolution of monogyny.     

甜菜夜蛾交配行为和能力

在(27±1)℃,光周期L14∶D10的条件下对甜菜夜蛾I>Spodoptera exigua的交配行为及能力进行了研究。结果表明：成虫在羽化当晚即可进行交配,交配率以羽化后头三个晚上的较高(>82%),但从第4天起则显著下降。成虫一天中的交配时间出现于23:30～05:30之间,交配高峰出现在01:30～02:30和03:00～04:00 之间, 其中以第1高峰的发生频率较高。成虫交配持续时间从22～191 min不等,但以30～60 min的为多(40.8%, n=97), 60～90 min的次之(19.4%),超过180 min的较少(10.2 %)。另外,交配持续时间与蛾龄紧密相关。蛾龄越大,交配持续的时间越长,且差异显著。雄蛾一生的交配能力由1～11次不等,但受性比的影响显著：在性比为1∶1的条件下,雄蛾平均交配次数仅为3.0 次,而在2♀∶1♂至5♀∶1♂时,则增加到5.1～6.0 次。雌蛾交配比例及次数受性比的影响也很大：没有交配的雌蛾比例从1∶1时的8.3%增加到5♀∶1♂时的32%,仅交配一次的比例从16.7%增加到38.7%,而交配≥5 次的比例则从 25%下降到0。最后,对这些结果在甜菜夜蛾防治中应用的可能性进行了讨论。     

小地老虎的交配行为和能力

在温度为(25±1)℃、相对湿度为70%±7%、光周期(L∶D)为14∶10h的条件下对小地老虎Agrotis ypsilon(Rottemberg)的交配行为和能力进行研究。结果表明:成虫在羽化后1d才进行交配。雄蛾和雌蛾都可以多次交配。交配能力受性比的影响很大,当1头雄蛾仅与1头雌蛾相处时,其交配能力低;当1头雄蛾与多于2头的雌蛾在一起时或1头雌蛾与多于2头的雄蛾在一起时,交配能力则显著增加。还讨论了该研究结果应用的可能性。     

Offspring sex ratio allocation in the parasitic jaeger: selection for pale females and melanic males?

The maintenance of plumage color polymorphism in the parasiticjaeger (Stercorarius parasiticus) is still not well understood.Earlier studies indicated that selection may favor pale femalesand melanic males. If so, females would maximize their fitness,producing pale female and melanic male offspring. We thereforepredicted that females might bias their offspring sex ratiotoward daughters in pale pairs and toward sons in melanic pairs.Females might also choose to mate assortatively in relationto plumage color, thereby maximizing the probability of producingeither pale or melanic offspring. Because females are largerthan males, differential rearing costs may affect the offspringsex ratio independent of parental plumage color. We examinedoffspring sex ratio allocation, breeding variables indicativeof parental quality, and mating pattern in relation to plumagecolor in a colony of parasitic jaegers in northern Norway. Jaegerstended to mate assortatively in relation to plumage color. Thereproductive performance declined with season, and matched pairsappeared to be of lower quality than mixed pairs. The proportionof male offspring increased with hatching date in matched paleand mixed pairs, whereas the situation was reversed in matchedmelanic pairs. Matched pale pairs produced an overall surplusof favorable pale but costly daughters despite their lower quality,while melanic pairs produced a surplus of favorable melanicsons. However, differential offspring rearing costs and parentalrearing capacity may have additionally affected the realizedoffspring sex ratio. Mixed pairs producing an overall surplusof pale and melanic daughters allocated their resources accordingto differential rearing costs and parental quality only. Wesuggest that both strategies of sex ratio allocation togetherwith differences in reproductive success in matched versus mixedpairs may have a balancing effect on the mating pattern betweenplumage morphs and may contribute to the maintenance of thecolor polymorphism in this species.