Mating frequency and reproductive success in an income breeding moth,Mnesampela privata

The frequency of mating in insects is often an important determinant of female reproductive output and male sperm competition. In Lepidoptera that provide male nutrients to the female when mating, it is hypothesized that polyandry may be more prevalent. This is thought to be especially so among species described as income breeders; that is, in species who do not derive all their nutrients for reproductive output entirely from the resources obtained during the larval stage. We selected the geometrid moth, Mnesampela privata (Guenée) (Lepidoptera: Geometridae), to examine this hypothesis further. We found this species was best characterized as an income breeder with female weight on emergence positively correlated with total egg load but not with the number of eggs laid. Further, in accord with income breeders, females emerged with a partially developed egg load and lifetime fecundity was positively correlated with the number of oviposition days. However, in the laboratory we found that incidence of repeated matings or polyandry was rare. When moths were paired singly over their lifetime, only 4% of mated females multiple mated. When females were paired with three males concurrently, female mating success increased from 60 to 81% with multiple mating among mated females increasing to just 15%. Dissection of wild caught M. privata found that polyandry levels were also low with a maximum of 16.4% of females collected at any one time being multiple mated. In accord with theory, mating significantly increased the longevity of females, but not of males, suggesting that females acquire essential resources from male ejaculates. Despite this, multiple mated females showed a trend toward decreasing rather than increasing female reproductive output. Spermatophore size, measured on death of the female, was not correlated with male or female forewing length but was negatively correlated with the number of fertile eggs laid and female longevity. Smaller spermatophore width may be related to uptake of more nutrients by the female from a spermatophore. We discuss our findings in relation to income breeding and its relationship to polyandry in Lepidoptera.     

Food fight: sexual conflict over free amino acids in the nuptial gifts of male decorated crickets

In decorated crickets, Gryllodes sigillatus, the spermatophore that a male transfers at mating includes a gelatinous spermatophylax that the female consumes, delaying her removal of the sperm‐filled ampulla. Male fertilization success increases with the length of time females spend feeding on the spermatophylax, while females may benefit by prematurely discarding the spermatophylaxes of undesirable males. This sexual conflict should favour males that produce increasingly appealing spermatophylaxes, and females that resist this manipulation. To determine the genetic basis of female spermatophylax feeding behaviour, we fed spermatophylaxes to females of nine inbred lines and found that female genotype had a major influence on spermatophylax feeding duration. The amino acid composition of the spermatophylax was also significantly heritable. There was a positive genetic correlation between spermatophylax feeding duration and the gustatory appeal of the spermatophylax. This correlation suggests that genes expressed in males that produce more manipulative spermatophylaxes are positively linked to genes expressed in females that make them more vulnerable to manipulation. Outbred females spent less time feeding on spermatophylaxes than inbred females, and thus showed greater resistance to male manipulation. Further, in a nonspermatophylax producing cricket (Acheta domesticus), females were significantly more prone to feeding on spermatophylaxes than outbred female Gryllodes. Collectively, these results suggest a history of sexually antagonistic coevolution over the consumption of nuptial food gifts.     

Structural evidence why males of Panorpa liui offer prey rather than salivary mass as their nuptial gift

Ma, N. and Hua, B. 2010. Structural evidence why males of Panorpa liui offer prey rather than salivary mass as their nuptial gift. —Acta Zoologica (Stockholm) 92 : 398–403. The scorpionflies are considered as ideal model animals for the study of mating systems in insects. The males generally offer both prey and salivary mass as nuptial gifts to the females during copulation. Our field observations show that Panorpa liui is peculiar because the males offer only prey rather than salivary secretions as nuptial gift. Through anatomical and histological examinations, the salivary glands of P. liui were found to be devoid of sexual dimorphism in Panorpa for the first time. Both the male and female P. liui bear simple salivary glands, which are only composed of a common duct and two short sac‐like glands. This is the first attempt to explore the relationship between the salivary glands and the mating tactics from the structural aspect in Panorpa, speculating that the simple structure of the male salivary glands in P. liui might be responsible for its failing to produce salivary mass as a nuptial gift during copulation. Compared with Boreidae, Meropidae, Bittacidae and Panorpidae, we presume that the absence of sexual dimorphism of the salivary glands might represent a plesiomorphy in P. liui. The origin and evolutionary process of the nuptial gift behaviour are tentatively speculated in Panorpa.     

雄性峨眉髭蟾“胡子”的组织结构特征

采用石蜡切片与苏木精-伊红染色及扫描电镜,对雄性峨眉髭蟾Leptobrachium boringii的角质刺及其周边皮肤进行了显微结构和亚显微结构的观察。显微结构观察发现,峨眉髭蟾的角质刺属于皮肤衍生物,突起呈倒"V"形。角质刺由表皮和真皮构成,表皮为复层扁平上皮,可分成4层;最外层细胞角质化,细胞轮廓不清,被染成深红色。真皮由疏松结缔组织构成,分辨不出致密层与疏松层,其内未见皮肤腺,但有少量色素细胞与毛细血管分布。表皮嵴伸入到真皮层,在以往的无尾两栖类研究中未见报道。角质刺基部可见皮肤褶翻起将其包裹在内,皮肤褶向上延伸形成角质刺。扫描电镜观察表明,角质刺顶端呈锥形的"小山丘"状,表面可分辨出表皮细胞轮廓,细胞为呈覆瓦状排列的角质化细胞。角质刺与皮肤交界处为多边形的角质化细胞。角质化上皮细胞的上表面与下表面均具有凹凸不平的花纹结构,细胞之间以镶嵌的方式连接。     

Female preference for male courtship flashes in Photinus ignitus fireflies

In Photinus fireflies, males produce spontaneous bioluminescentcourtship flashes. Females preferentially respond to particularmale flashes with flashes of their own. This study exploredvariation in female flash responsiveness as a function of maleflash duration, female condition, lantern size, and lanterndistance, as well as the relationship between male characteristicsand spermatophore mass in Photinus ignitus fireflies. We determinedfemale preference by scoring female flash response to simulatedmale flashes and determined variation in overall female flashresponsiveness for laboratory-mated, laboratory-fed, and controlP. ignitus females. Flash duration, lantern size, and body masswere recorded for field-collected males. Males were then matedto determine spermatophore mass. Females exhibited greater preferencefor artificial flashes representing the upper range of conspecificmale flash duration and lantern size as well as flashes producedat a closer distance. Both laboratory-mated and laboratory-fedP. ignitus females showed lower overall responsiveness acrossall flash durations relative to control females that did notmate or feed in the laboratory. Male flash duration predicteda significant proportion of the variation in spermatophore massfor early-season males. These results suggest that female Photinusignitus may prefer long flashes in order to obtain the directbenefit of larger spermatophores and may adjust their overallflash responsiveness as the relative importance of this benefitvarieswith changing female condition.     

Monandry and polyandry as alternative lifestyles in a butterfly

Butterflies show considerable variability in female mating frequency, ranging from monandrous species to females mating several timesin their lifetime. Degree of polyandry also varies within species,with some females only mating once and others mating multiply.Previous studies have shown that one reason for female multiplemating is to obtain nutritious male donations that both increasethe longevity of females and result in higher lifetime fecundity.Despite the presence of male nutrient donations, some femalesof the green-veined white butterfly (Pieridae: Pieris napi)never mate more than once. In this study, we examined thisapparent paradox. We assessed to what degree polyandry is undergenetic control by a full-sib analysis, and we also estimatedthe broad sense heritability of female lifetime fecundity in singly mated females. Both polyandry and lifetime fecundityhave a genetic component. However, degree of polyandry appearsto be traded off against reduced longevity when denied theopportunity to mate more than once. It is possible that femaleP. napi display different reproductive strategies, with somefemales relying on male donations to realize their potentialfecundity and others relying on their own resources for egg production. In nature, polyandrous females may be preventedfrom mating multiply due to unfavorable weather. We discussthe possibility that the trade-off between degree of polyandryand life span when singly mated may affect the maintenanceof genetic variability in female mating frequency in this species.Possible reasons for these different reproductive strategiesare discussed.     

To feed or to wrap? Female silk cues elicit male nuptial gift construction in a semiaquatic trechaleid spider

By wrapping prey and offering it as a nuptial gift, males can obtain mating and/or parental benefits despite some costs. Males of the Neotropical semiaquatic spider Paratrechalea ornata (Trechaleidae) offer females a nuptial gift consisting of a prey item wrapped in silk. What stimulus inhibits males from feeding and elicits gift construction? We hypothesized that signals associated with female silk threads could affect decision-making by males. We investigated three groups of males carrying a captured prey under different experimental treatments. In the treatment S, males were exposed to an arena with female silk; in SF, males were exposed to both silk and a female confined in a cell, and in the control group, males were exposed to a clean arena. Gift construction was observed only in the S and SF groups, with a similar occurrence rate. After touching females (SF group), males did not change their pattern of gift construction. Gift construction occurrence increased with male and female age. The results lead us to assume that the existence of chemical cues associated with female silk elicits male searching behaviour and gift construction, allowing males to decide between eating or wrapping prey according to the possibility of a sexual encounter. Anticipating gift construction, males are ready to mate, diminishing the risks of predation, female desertion or male–male scramble competition. The effect of age on behavioural variation and the rate of construction is discussed.     

Interspecific variation in ejaculate allocation and associated effects on female fitness in seed beetles

When ejaculates are costly to produce, males are expected to allocate their ejaculate resources over successive matings in a manner that optimizes their reproductive success and this may have important consequences for their mates. In seed beetles (Coleoptera; Bruchidae), ejaculates vary in size across species from weighing less than 1%, up to as much as 8%, of male body weight. Ejaculates contain not only sperm but also a range of additional substances and females in some species gain benefits from receiving large ejaculates. Male ejaculate allocation may thus affect female fitness. Here, we first characterized the pattern of male ejaculate allocation over successive matings in seven-seed beetle species. We then assessed how this allocation affected female fitness in each species. Although females generally benefited from receiving large ejaculates, the interspecific variation observed both in ejaculate allocation patterns and in their effects on female fitness was remarkably large considering that the species studied are closely related. Our analyses suggest that variation in ejaculate composition is the key, both within and across species. We discuss possible causes for this variation and conclude that coevolution between male ejaculates and female utilization of ejaculate substances has apparently been rapid in this clade.     

Female remating in butterflies: interaction between female genotype and nonfertile sperm

Female mating rate is fundamental to evolutionary biology as it determines the pattern of sexual selection and sexual conflict. Despite its importance, the genetic basis for female remating rate is largely unknown and has only been demonstrated in one species. In paternally investing species there is often a conflict between the sexes over female mating rate, as females remate to obtain male nutrient donations and males try to prevent female remating to ensure high fertilization success. Butterflies produce two types of sperm: fertilizing, eupyrene sperm, and large numbers of nonfertile, apyrene sperm. The function of apyrene sperm in the polyandrous, paternally investing green‐veined white butterfly, Pieris napi, is to fill the female’s sperm storage organ thereby reducing her receptivity. However, there is large variation in number of apyrene sperm stored. Here, I examine the genetic basis to this variation, and if variation in number of apyrene sperm stored is related to females’ remating rate. The number of apyrene sperm stored at the time of remating has a genetic component and is correlated with female remating tendency, whereas no such relationship is found for fertilizing sperm. The duration of the nonreceptivity period in P. napi also has a genetic component and is inversely related to the degree of polyandry. Sexual conflict over female remating rate appears to be present in this species, with males using their apyrene sperm to exploit a female system designed to monitor sperm in storage. Ejaculates with a high proportion of nonfertile sperm may have evolved to induce females to store more of these sperm, thereby reducing remating. As a counter‐adaptation, females have evolved a better detection system to regain control over their remating rate. Sexually antagonistic co‐evolution of apyrene sperm number and female sperm storage may be responsible for ejaculates with predominantly nonfertile sperm in this butterfly.