Male inbreeding status affects female fitness in a seed-feeding beetle

Inbreeding generally reduces male mating activity such that inbred males are less successful in male-male competition. Inbred males can also have smaller accessory glands, transfer less sperm and produce sperm that are less motile, less viable or have a greater frequency of abnormalities, all of which can reduce the fertilization success and fitness of inbred males relative to outbred males. However, few studies have examined how male inbreeding status affects the fitness of females with whom they mate. In this study, we examine the effect of male inbreeding status (inbreeding coefficient f = 0.25 vs. f = 0) on the fecundity, adult longevity and the fate of eggs produced by outbred females in the seed-feeding beetle, Callosobruchus maculatus. Females mated to inbred males were less likely to lay eggs. Of those that laid eggs, females mated to inbred males laid 6-12% fewer eggs. Females mated to inbred males lived on average 5.4% longer than did females mated to outbred males, but this effect disappeared when lifetime fecundity was used as a covariate in the analysis. There was no effect of male inbreeding status on the proportion of a female's eggs that developed or hatched, and no evidence that inbred males produced smaller nuptial gifts. However, ejaculates of inbred males contained 17-33% fewer sperm, on average, than did ejaculates of outbred males. Our study demonstrates that mating with inbred males has significant direct consequences for the fitness of female C. maculatus, likely mediated by effects of inbreeding status on the number of sperm in male ejaculates. Direct effects of male inbreeding status on female fitness should be more widely considered in theoretical models and empirical studies of mate choice.     

Ejaculate size, second male size, and moderate polyandry increase female fecundity in a seed beetle

Several hypotheses have been proposed to explain the evolutionof polyandry in species that provide nuptial gifts. When nuptialgifts are in the form of nutritional elements in the ejaculateand ejaculate size is correlated with male body size, femalescan accrue both direct (nutritional) and indirect (genetic)benefits from multiple mating. We examined remating decisionsin females of the seed beetle Stator limbatus and, using pathanalysis, examined the effects of male body size on the sizeof his ejaculate, the amount of ejaculate that was successfullytransferred to females, and the overall effect of these variableson female fecundity. Larger males produced larger ejaculatesand consequently transferred a larger ejaculate to females,but the effects on female fecundity differed between the females'first and second mates. Both larger first and second males wereable to transfer more of their ejaculate to females than weresmaller males. Both the total amount of ejaculate transferredby these males and polyandry (number of matings) were positivelycorrelated to female fecundity independently of each other.However, larger second males were more successful at stimulatingfemale fecundity independently of how much ejaculate they transferred.We also provide evidence that females are choosy during theirsecond mating opportunity. Both female choosiness and higherfemale investment after mating with larger second males suggestthat females may benefit from both direct and indirect effectsfrom multiple mating. We also conclude that male body size isunder both directional fecundity selection and directional sexualselection.     

The effects of copulation duration in the bruchid beetle Callosobruchus maculatus

Control over copulation duration is a potentially importantgenerator of sexual conflict that has received little empiricalattention. The copulatory behavior of the bruchid beetle Callosobruchusmaculatus may reflect a sexual conflict over copulation duration.Males have spines on their intromittent organs that puncturethe female reproductive tract, and females kick their matesduring copulation. If females are prevented from kicking, copulationslast longer and the injuries females sustain are more severe.Males supposedly use the spines as anchors to prolong copulationduration, and females kick to terminate copulations. We manipulatedcopulation duration experimentally and quantified its effectson male and female fitness components to test whether or notthere is a conflict over copulation duration in C. maculatus.Females did not suffer from long copulations but instead experiencedincreased lifetime fecundity. Ejaculate size increased withcopulation duration, and females apparently derive materialbenefits from the ejaculates. Males that mated first and hadlong copulations were relatively unsuccessful when competingwith sperm from other males. However, there was a trend forfemale remating propensity to decrease with long copulationdurations, and first males may therefore also benefit from longcopulations. The copulation duration of the second male to matedid not have a significant effect on sperm precedence. We concludethat even though it seems likely that the male spines have evolvedto act as an anchor during copulation, there seems to be littleconflict over copulation duration per se in C. maculatus.     

Protein and carbohydrate intake influence sperm number and fertility in male cockroaches,but not sperm viability

It is commonly assumed that because males produce many, tiny sperm, they are cheap to produce. Recent work, however, suggests that sperm production is not cost-free. If sperm are costly to produce, sperm number and/or viability should be influenced by diet, and this has been documented in numerous species. Yet few studies have examined the exact nutrients responsible for mediating these effects. Here, we quantify the effects of protein (P) and carbohydrate (C) intake on sperm number and viability in the cockroach Nauphoeta cinerea, as well as the consequences for male fertility. We found the intake of P and C influenced sperm number, being maximized at a high intake of diets with a P : C ratio of 1 : 2, but not sperm viability. The nutritional landscapes for male fertility and sperm number were closely aligned, suggesting that sperm number is the major determinant of male fertility in N. cinerea. Under dietary choice, males regulate nutrient intake at a P : C ratio of 1 : 4.95, which is midway between the ratios needed to maximize sperm production and pre-copulatory attractiveness in this species. This raises the possibility that males regulate nutrient intake to balance the trade-off between pre- and post-copulatory traits in this species.     

Scrotal dimensions and ejaculate characteristics of three breeds of sheep in tropical Nigeria

Scrotal circumference and semen characteristics of three breeds of sheep (Udda, Balami and Yankasa) indigenous to Nigeria and Southern Guinea Savannah zones of Africa were compared. The age, body weight, scrotal circumference and spermiogram of the rams were studied by standard techniques. The mean age, body weight, and scrotal circumference of the three breeds were not comparable with significant interbreed, but were with significant intrabreed differences. The mean ejaculate concentration of sperm cells (x 10 /ml) were: Udda, 3.8 +/- 0.050, Balami, 4.1 +/- 0.32, Yankasa, 4.5 +/- 0.11. The mean morphological sperm cell abnormalities for the Udda, Balami and Yankasa were; 7.5 +/- 2.1%, 4.5 +/- 0.58% and 6.0 +/- 0.87%, respectively, with significant inter- and intrabreed differences. There were significant intrabreed differences in the other semen traits, i.e., percent of live cells, percent of motility, mean volume and mean concentration. In all the breeds of sheep studied, the scrotal circumference and spermiogram were comparable to, and within the range reported for the exotic breed of rams.     

Condition-dependent ejaculate size and composition in a ladybird beetle

Sexually selected male ejaculate traits are expected to depend on the resource state of males. Theory predicts that males in good condition will produce larger ejaculates, but that ejaculate composition will depend on the relative production costs of ejaculate components and the risk of sperm competition experienced by low- and high-condition males. Under some conditions, when low condition leads to poorer performance in sperm competition, males in low condition may produce ejaculates with higher sperm content relative to their total ejaculate and may even transfer more sperm than high-condition males in an absolute sense. Previous studies in insects have shown that males in good condition transfer larger ejaculates or more sperm, but it has not been clear whether increased sperm content represents a shift in allocation or simply a larger ejaculate, and thus the condition dependence of ejaculate composition has been largely untested. We examined condition dependence in ejaculate by manipulating adult male condition in a ladybird beetle (Adalia bipunctata) in which males transfer three distinct ejaculate components during mating: sperm, non-sperm ejaculate retained within the female reproductive tract, and a spermatophore capsule that females eject and ingest following mating. We found that high condition males indeed transferred larger ejaculates, potentially achieved by an increased rate of ejaculate transfer, and allocated less to sperm compared with low-condition males. Low-condition males transferred ejaculates with absolutely and proportionally more sperm. This study provides the first experimental evidence for a condition-dependent shift in ejaculate composition.     

Male crickets adjust ejaculate quality with both risk and intensity of sperm competition

Sperm competition theory predicts that males should increase their expenditure on the ejaculate with increasing risk of sperm competition, but decrease their expenditure with increasing intensity. There is accumulating evidence for sperm competition theory, based on examinations of testes size and/or the numbers of sperm ejaculated. However, recent studies suggest that ejaculate quality can also be subject to selection by sperm competition. We used experimental manipulations of the risk and intensity of sperm competition in the cricket, Teleogryllus oceanicus. We found that males produced ejaculates with a greater percentage of live sperm when they had encountered a rival male prior to mating. However, when mating with a female that presented a high intensity of sperm competition, males did not respond to risk, but produced ejaculates with a reduced percentage of live sperm. Our data suggest that males exhibit a fine-tuned hierarchy of responses to these cues of sperm competition.     

The effect of remating on sperm number in the spermatophores of Teleogryllus commodus (Gryllidae)

Factors controlling sperm production in members of the Orthoptera have not been fully elucidated. In this study, the influence of intermating interval and ad libidum mating on sperm number was investigated in black field crickets (Teleogryllus commodus). Remating at a variety of time intervals was not characterized by a significant change in sperm number compared with the first mating. Ad libitum mating (i.e., continuous availability of unmated females) had two main effects on spermatophore production and sperm number: first, there was a trend toward increased time between copulations with each successive remating, and second, the number of spermatozoa encapsulated in the transferred spermatophore declined after most rematings, with 61.8% of the initial sperm number being produced for the second spermatophore and 51.3% of the initial sperm number being produced for the third. The decrease in mean sperm number was accompanied by increased variance in sperm number in later rematings. This study suggests that males are willing to suffer a decrease in sperm number if a mating opportunity occurs before the completion of sperm production.     

Field mating rate of female meadow grasshoppers, Chorthippus parallelus, estimated from sperm counts

Abstract.  1. Female mating frequency is an important life-history component in many insect species. It has been suggested that its laboratory measurement may frequently represent an overestimation of the natural situation because laboratory females have little opportunity to avoid matings. Here, numbers of sperm stored by field-collected females are investigated in order to address whether this method is suitable for estimating field mating frequencies.
2. Data on sperm numbers stored by females and their estimated age based on mandible abrasion were fitted to a simple mechanistic model to obtain estimates of: (i) remating interval; (ii) ejaculate size, and (iii) the rate of sperm loss from the female sperm store. Females were calculated to remate every 5.9–7.0 days. By contrast, sperm numbers of field-collected females did not exceed ejaculate size, which would have resulted in the false conclusion that females mate only once.
3. In the laboratory, females first mated when aged 4–11 days and remated approximately every 2.6 days. Because females are not restricted by mate encounters under these conditions, this confirms the notion that female mating rates are likely to be lower in the field than in the laboratory. Such reduced field mating rates should be taken into account when predicting ecological or evolutionary parameters based on laboratory observed mating rates.     

Ejaculate size varies with socio-sexual situation in an insect

Abstract.

• 1 Males operate within a finite energy budget and cannot produce limitless supplies of sperm. On the other hand, when a female mates with a second male while still containing fertile sperm from a rival male, selection should favour the male that inseminates more sperm. Optimal strategy should thus be for males to exercise discretion in the allocation of sperm to individual females. Assuming the outcome of sperm competition to be based on either the raffle or kamikaze principles, the sperm competition hypothesis predicts a positive association between the probability that the sperm will find themselves in competition with sperm from rival males and the number of sperm inseminated.
• 2 The beetle, Tenebrio molitor L., behaves in accordance with this hypothesis. Males accompanied by a rival male before and during mating inseminate more sperm per ejaculate than unaccompanied males. Accompanied males are also faster to initiate mating and more likely to show post-copulatory guarding. Adjustment of number of sperm inseminated was shown by males subjected to both long-term (5 days) and short-term (5 min) exposure to potential intrasexual competitors. Individual males exposed to both levels also demonstrated the ability to adjust their ejaculate according to socio-sexual situation.
• 3 We conclude that male T.molitor adjust the number of sperm they inseminate according to some perception of the risk of sperm competition.

     

Variation in nuptial gift quality in bush crickets (Orthoptera: Tettigoniidae)

Males of many insect species provide the female, during courtshipand copulation, with a nuptial gift consisting of a prey itemor synthesized material (e.g., spermatophores). The studiesperformed so far have mainly focused on effects of nuptial giftsize on male and female reproductive success. However, the qualityof the nuptial gift can differ substantially between taxa andmay potentially have a large impact on male and female reproductiveperformance. In this study the effects of. variation in dieton nuptial gift quality is investigated in several bush cricketspecies with different diets. The effect of diet on nuptialgift quality (e.g., protein in the spermatophylax) and femalereproductive output and, in turn, die effect of variation inspermatophylax quality on female reproductive output are investigated.Female reproductive output and male spermatophore size weremainly found to be influenced by differences in diet betweenspecies. Spermatophylax quality (i.e., protein concentration)was also correlated with differences in diet. There was a largevariation in protein content of the spermatophylax widiin aswell as between species. Moreover, larger spermatophylaxes hada lower protein concentration, indicating a possible trade-offbetween spermatophylax size and quality. Consequendy, productionof larger spermatophylaxes, required for protection of the male'ssperm carrying ampulla during insemination, can lead to a reducedprotein concentration, because the total amount of protein maybe limited. This pattern is also consistent with die idea diatthe spermatophylax functions primarily to ensure sperm transfer.Finally, there was no correlation between the amount of proteinin the spermatophylax and female reproductive output eitheracross diets or within each diet category, further supportingthe finding that female reproductive output is mainly affectedby differences in diet.