Assessing mate size in the red swamp crayfish Procambarus clarkii: effects of visual versus chemical stimuli

1. Mate assessment requires an efficient system of information exchange between the sexes and often relies on several forms of communication. Both sexes of the crayfish, Procambarus clarkii , select a mate on the basis of its body size, independently of chelar size/symmetry and dominance status, large size being a proxy for a high quality partner. Here, we explored the effects that visual and chemical stimuli, emitted alone or in combination, exert on the assessment of size of a potential mate.
2. We followed a binary choice test paradigm, in which two male or female 'targets', of either large or small size, were simultaneously presented to a female or a male 'chooser'. We recorded the first target visited, the total duration of the visits per target, and the behaviour of the chooser when approaching the target area.
3. Our results show that females require a combination of visual and chemical stimuli to select the larger male. A more complex pattern was found when males were the choosers. While visual and chemical cues together rendered them willing to mate with the larger female, their initial choice and the total time spent near her depended only on smell. In mate assessment by P. clarkii , visual and chemical information seem to act as 'non-redundant signals'.     

Sequential mate encounters: female but not male body size influences female remating behavior

Whether and how individuals choose sequentially among matesis an important but largely neglected aspect in sexual selectionstudies. Here, we explore female remating behavior in the cellarspider Pholcus phalangioides. We focus on body size as one ofthe most important traits involved in mate choice. Large andsmall females (n = 216) were double mated with large or smallmales in all eight possible combinations. All females copulatedwhen virgin, but only 82% accepted a second male. The chanceof a female remating was not significantly predicted by thebody size of the second or first male or by the size differencebetween the two. In contrast, a previous study demonstrateda male size effect in that larger males monopolized femalesuntil egg laying when two males of different sizes were present.We suggest that sequential encounters are more common undernatural conditions than male monopolization of females becauseestimates of concurrent multiple paternity together with observationsin a natural population do not favor mate guarding as the predominantmating strategy in this species. It follows from our study thatthe intensity of sexual selection on male size may be greatlyoverestimated when using a competitive laboratory setting fora species in which females generally encounter mates in a sequentialfashion. Female remating probability was significantly predictedby female size, with large females remating with higher probabilitythan small females. Thus, when mating with large females, malesmay gain higher fertilization success through increased femalefecundity but also face a higher sperm competition risk.     

The effect of male size on receptivity in femaleLucilia cuprina (Diptera: Calliphoridae)

The first five matings by both large and small L. cuprinamales switched off receptivity in over 90% of females for 7 days after their initial mating. Small males were virtually unable to switch off females after five matings, whereas the fifth to tenth matings by large males rendered nearly two-thirds of females unreceptive. Mating duration of large and small males was about 11 min even after numerous matings. Given the rarity of field virgins and the temporal and spatial variability of female-required resources, larger males may enjoy greater mating success due to their ability to switch off many females in succession. Virgin males preferred to mate with nonvirgin females larger than themselves; males paired with females smaller than themselves adopted mate-rejection behavior typical of unreceptive females.     

Effect of body size and larval experience on mate preference in Helicoverpa armigera (Hübner) (Lep., Noctuidae)

Abstract:  We studied the mating selection in the cotton bollworm, Helicoverpa armigera (Hübner), in relation to body size and larval diet in the laboratory. When provided with an artificial diet at larval stage, weight, body and forewing length did not affect the probability of a male/female moth being selected for mating, but the abdominal width of selected female moths was significantly wider than that of non-selected female moths. 30 female moths were dissected and number of eggs was counted after mating, and there was a correlation between the abdominal width and egg number. There was also significant difference of weight loss between selected and non-selected male/female moths after the mating. The effect of operational sex ratio on mating latency and copulation duration were tested, and the result indicated that mating latency of male selection was significantly longer than that of female selection, but the difference of copulation duration was not significant. Cotton, corn and peanut plants were provided to larvae to test the effect of larval host plant experience on mate choice. When cotton- and peanut-fed moth severed as potential partners, both female and male of cotton-fed moths significantly preferred cotton- to peanut-fed moths for mating. The possible reasons for mate preference based on larval host plant experience may account for host plants attributes on sex pheromone variation and sexual maturity. These findings may impact Bacillus thuringiensis resistance management.     

Sequential mate choice by multiply mating smooth newts: females become more choosy

In some species, females sequentially mate with different maleswithin a single mating period, store sperm until the eggs areeventually fertilized, and gain no other resources from themales. Halliday hypothesized that, for such species, a femalecould ensure fertilization of her eggs by mating with the firstmale that she encounters; thereafter, she can maximize the qualityof her progeny by sampling further males and by mating onlywith males of higher quality than previously mated males. Thishypothesis predicts that females' choosiness will increase asthe breeding season progresses. We tested this prediction ofHalliday's hypothesis by examining mate choice by female smoothnewts (Triturus vulgaris vulgaris). Males of this species developa dorsal crest during the courtship season. Crest height variesbetween males and is potentially an indicator of male quality.Initially, female smooth newts were equally willing to matewith males with low or high crests. However, in their secondmating, females remated only with high-crested males. Theseresults support our prediction and are consistent with Halliday'shypothesis. If crest height in smooth newts is an indicatorof quality, this change in females' mate choice criterion allowsfemales both to initiate egg-laying very early in the seasonand, subsequently, to mate preferentially with higher qualitymates     

Precision in sex allocation is influenced by mate choice in Drosophila melanogaster

Theory predicts that a 1 : 1 sex ratio is favoured in the absence of countervailing selection pressures. In an experiment with Drosophila melanogaster, we found significantly greater variation in the offspring sex ratios of freely mated flies than would be expected by the binomial distribution. In a surprise result, control flies given no mate choice exhibited significant under-dispersal in their sex ratio variation, possibly from sperm limitation. Both treatments, however, produced populations with a 1 : 1 sex ratio. This supports the hypothesis that sexually antagonistic selection for reproductive success in sons, and fecundity in daughters, may overcome selection for an equal sex ratio. Such precision in sex allocation may allow for the maintenance of genetic variation underlying trade-offs between male and female reproductive success.     

Preferred males are not always good providers: female choice and male investment in tree crickets

Female tree crickets (Oecanthus nigricornis) prefer large malesbut do not receive larger glandular courtship gifts from thesemales. This finding is puzzling from both the male and femaleperspectives, because females should prefer males providingmore direct benefits, and because males who provide larger giftsachieve higher insemination success. We tested for differencesin the quality of male secretions and found that larger malesprovided more proteinaceous food gifts than did rivals, whichcould explain why they are preferred by females. The preferencein turn could cause depletion of food gift reserves in favoredmales, because natural remating rates are high and because evena single feeding bout negatively affects glandular stores. Mostintriguingly, we showed that preferred males can adaptivelydecrease the size of courtship food-gifts provided (in orderto conserve gifts for future mating events) when they perceivethat the probability of multiple future mating opportunitiesis high. Thus, the elevated mating rates of preferred males(both before and after a focal mating event) could account forthe small size of their courtship food-gifts.     

Nestmateship and body size do not influence mate choice in males and females: A laboratory study of a primitively eusocial wasp Ropalidia marginata

We investigated the effect of nestmateship and body size on mate selection through a choice based assay in the primitively eusocial wasp Ropalidia marginata. A recent study has shown that male and female R. marginata mate with their nestmates and non-nestmates with equal probability if no choice is available. That study could also not detect any influence of body size on mating probability in the absence of choice. To confirm that the same results can be obtained even when the wasps have a choice, we offered a choice of two virgin partners either to a virgin test male or to a virgin test female and measured the probability that the test individual would mate with any particular partner based on nestmateship or body size. We show here that even when a choice is available, neither male nor female test wasps base their mate choice on the nestmateship or body size of the partner. We therefore suggest that the natural mating habit of these wasps is sufficiently promiscuous and not constrained by such factors as nestmateship and body size.     

The role of nocturnal vision in mate choice: females prefer conspicuous males in the European tree frog (Hyla arborea)

Nocturnal frog species rely extensively on vocalization for reproduction. But recent studies provide evidence for an important, though long overlooked, role of visual communication. In many species, calling males exhibit a conspicuous pulsing vocal sac, a signal bearing visually important dynamic components. Here, we investigate female preference for male vocal sac coloration—a question hitherto unexplored—and male colour pattern in the European tree frog (Hyla arborea). Under nocturnal conditions, we conducted two-choice experiments involving video playbacks of calling males with identical calls and showing various naturally encountered colour signals, differing in their chromatic and brightness components. We adjusted video colours to match the frogs'' visual perception, a crucial aspect not considered in previous experiments. Females prefer males with a colourful sac and a pronounced flank stripe. Both signals probably enhance male conspicuousness and facilitate detection and localization by females. This study provides the first experimental evidence of a preference for specific vocal sac spectral properties in a nocturnal anuran species. Vocal sac coloration is based on carotenoids and may convey information about male quality worthwhile for females to assess. The informative content of the flank stripe remains to be demonstrated.     

Effects of a parasitic nematode on male mate choice in a livebearing fish with a coercive mating system (western mosquitofish, Gambusia affinis)

I examined the effects of the parasitic larval nematode, Eustrongylides ignotus, on male mate choice in the western mosquitofish, Gambusia affinis. I hypothesized that parasite presence influences male mate choice either directly (via reduction in male mating behavior due to presence of parasite in females) or indirectly (via reduction in male mating behavior due to reduced condition of infected females). Specifically, I tested the predictions that (1) males would mate preferentially with uninfected over infected females (scoring both mating attempts and association time with females); (2) parasitized females would be in poorer condition than non-parasitized females (measured as soluble fat stores); and (3) parasitized females would have reduced fecundity (measured as number of developing embryos). Males preferred to mate with non-parasitized over parasitized females, but showed no differences in association time between females. The nematode did not decrease female body condition, but did decrease female mass, and appeared to decrease female fecundity via reduction in broods (# embryos). Results support that parasites affect male mate choice in mosquitofish; however, the mechanisms used by males to differentiate between parasitized and non-parasitized females remain untested. This study provides the first empirical evidence of parasite affects on male mate choice in livebearing fishes, and suggest a potentially important role for parasite-mediated sexual selection in organisms that use coercive mating as the primary mechanism of obtaining mates.     

Choosy females and indiscriminate males: mate choice in mixed populations of sexual and hybridogenetic water frogs (Rana lessonae, Rana esculenta)

For several decades, behavioral ecologists have studied theeffects of the environment on the behavior of individuals;but only fairly recently they have started to ask the reversequestion: how do the behavioral strategies of individuals affectthe composition and dynamics of populations and communities?Although intuitively obvious, this feedback from individualto higher levels is difficult to demonstrate, except in systemswith exceptionally fast and marked responses of the populationsto the behavior of its members. Such a system exists in sperm-dependentspecies. In European water frogs, for instance, successfulreproduction of a hybrid species (R. esculenta, genotype LR)requires mating with one of its parental species (R. lessonae,genotype LL), except in the rare cases where hybrids are triploid.The sexual host LL, however, should avoid matings with the sexual parasite LR, because the resulting LR offspring willeliminate the L genome from their germ line. In this studywe investigate how this conflict is solved. Since water froghybrids come in both sexes, rather than as females only likein other sperm-dependent systems, we performed the tests withboth females and males. One individual was given a choice betweentwo individuals of the opposite sex, one an LL and the otheran LR. In both species, females showed the predicted preferencefor LL males, whereas males did not discriminate between LLand LR females. On the individual level, we interpret the sexdifference in choosiness by the lower costs from mating withthe wrong species (LR) and the higher benefits from matingwith large individuals in males than in females. In "normal"species, male preference for large (i.e. more fecund) femalesis advantageous, but in this system such a choice can resultin mating with the larger LR females. With respect to the structureand dynamics of mixed populations, we discuss that the observed female preference is consistent with the higher mating successof LL males found in nature. Hence, mate female choice is astrong candidate for a mechanism promoting coexistence of thesperm-dependent hybrid and its sexual host. This confirms predictionsfrom previous theoretical models.     

Sexual size dimorphism and selection in the wild in the waterstrider Aquarius remigis: Body size,components of body size and male mating success

Sexual size dimorphism is assumed to be adaptive and is expected to evolve in response to a difference in the net selection pressures on the sexes. Although a demonstration of sexual selection is neither necessary nor sufficient to explain the evolution of sexual size dimorphism, sexual selection is generally assumed to be a major evolutionary force. If contemporary sexual selection is important in the evolution and maintenance of sexual size dimorphism then we expect to see concordance between patterns of sexual selection and patterns of sexual dimorphism. We examined sexual selection in the wild, acting on male body size, and components of body size, in the waterstrider Aquarius remigis, as part of a long term study examining net selection pressures on the two sexes in this species. Selection was estimated on both a daily and annual basis. Since our measure of fitness (mating success) was behavioral, we estimated reliabilities to determine if males perform consistently. Reliabilities were measured as ? statistics and range from fair to perfect agreement with substantial agreement overall. We found significant univariate sexual selection favoring larger total length in the first year of our study but not in the second. Multivariate analysis of components of body size revealed that sexual selection for larger males was not acting directly on total length but on genital length. Sexual selection for larger male body size was opposed by direct selection favoring smaller midfemoral lengths. While males of this species are smaller than females, they have longer genital segments and wider forefemora. Patterns of contemporary sexual selection and sexual size dimorphism agree only for genital length. For total length, and all other components of body size examined, contemporary sexual selection was either nonsignificant or opposed the pattern of size dimporhism. Thus, while the net pressures of contemporary selection for the species may still act to maintain sexual size dimorphism, sexual selection alone does not.     

Extra-pair mate choice in the female great tit <Emphasis Type="Italic">Parus major</Emphasis>: good males or compatible males

The good genes hypothesis and the genetic compatibility hypothesis are the two main hypotheses that focus on the genetic benefit that a female can gain through her choice of a mate. We tested the two hypotheses on extra-pair mating in the great tit, Parus major. We found that female great tits choose males on the basis of breast stripe width, which is in accordance with the good genes hypothesis. Although females chose less related extra-pair males, the evidence for female choice for compatible males was overall weak. However, our data suggest a post-copulatory mechanism of inbreeding avoidance. The observed individual inbreeding coefficient, F, was similar for within-pair offspring (WPO) and extra-pair offspring (EPO). The observed individual F of WPO was lower than the expected individual F, whereas the observed F of EPO was similar to what was expected. These results highlight the importance of processes after copulation for the outcome of female mate choice. Our study shows that in a system with apparent pre-copulatory female choice for good genes, a post-copulatory mechanism may still promote the production of offspring that carry compatible genes.     

The effects of body size on mating and reproduction in Brachinus lateralis (Coleoptera: Carabidae)

Abstract. 1. The causes and reproductive consequences of body size variation of Brachinus lateralis Dejean, a parasitic carabid beetle, were investigated.
2. Body size variation occurs within and between sites. Host size has a major influence on body size of the adult.
3. Fecundity is positively correlated with body size. Egg size is not correlated with body size.
4. Mating males tend to be larger than non-mating males. There is a positive correlation of body sizes in mating pairs.
5. Limited opportunity for host choice may maintain size variation despite the advantages of large size.
6. The non-random patterns of mating for a species without obvious intrasexual aggression suggest that subtle means of male-male competition or female choice may be important.     

By-product runaway evolution by adaptive mate choice: A behavioural aspect of sexual selection

Summary From a behavioural perspective on adaptive female choice, I developed a by-product runaway model of adaptive mate choice. The model illustrates the evolution of the tail size of peacocks. I consider the causal mechanisms of adaptive female choice: (1) why (ultimate reasons); (2) how (proximate mechanisms). Assumptions are developed based on these behavioural aspects. For (1) ultimate reasons, I assume that many male losers (low-fitness males) always occur due to genetic and environmental uncertainty (A-1). For (2) proximate mechanisms, I assume that losers tend to differ in the expression of a fitness-sensitive trait (an ultimate target, e.g. body size; A-2), that the fitness-sensitive trait correlates with a secondary sexual trait (a proximate cue, e.g. allometry in body size and tail size; (A-3), and that the cue trait has a genetic basis that is independent of the target trait (e.g. a genetic basis in tail ratio to body size; A-4). The model's results are: persistent female choice by means of a proximate cue (R-1); by-product selection on the independent genetic basis of the cue (R-2); and the non-adaptive or maladaptive runaway evolution of the male proximate cue (R-3). In this model, female mate preferences are non-arbitrary and adaptive, whereas the resulting evolution of male secondary sexual traits is non-adaptive in the sense of survival selection.