Evidence of female cryptic choice in crayfish

To test whether male body size affects female reproductive investment in the polygamous crayfish Procambarus clarkii, we described mating behaviour of virgin females paired with either small or large males, and analysed the number, size and weight of both eggs and juveniles sired by either types of male. Along with confirming the overt selection by females of larger mates, we found that the size and weight of both the eggs and the juveniles were higher when sired by larger fathers. This suggests that P. clarkii females exert a form of cryptic choice for large males, seemingly adjusting the quantity of egg deutoplasm in function of the mate body size. The question of why females spend time and energy to brood low-fitness offspring is finally raised.     

THE EFFECTS OF THE MATING SYSTEM ON PROGENY PERFORMANCE IN HYLA CRUCIFER (ANURA: HYLIDAE)

We performed a controlled mating experiment to determine whether genetic variation in larval traits in Hyla crucifer was predictable on the basis of mating status or body size of male parent. Larval growth rate was predictably related to body size of the sire. Males from the upper half of the body-size distribution sired offspring with 6% higher growth rates than those of offspring sired by males from the lower half of the body-size distribution. Offspring sired by males that obtained mates in nature had 3% higher growth rates than their half-siblings sired by males that did not mate in nature. Genetic variation for larval-period duration and size at metamorphosis was detected; however, neither mating status nor body size of sire could be used to predict values of these traits in the progeny. Although all three larval traits can affect fitness, there was no evidence that the offspring of some sires would always outperform the offspring of others in all three traits. The predictable association between adult male size and larval growth rate means that the H. crucifer mating system would have a directional effect on larval growth rate if male body size influences the outcome of male-male competition or female choice.     

Why do territorial male Tengmalm's owls fail to obtain a mate?

Non-breeding may occur because non-breeders are immature or somehow physiologically incapable of breeding, or because of a lack of resources (e.g. food resources, mating partners) needed to breed. There is, however, a lack of experimental evidence on whether bachelor males possessing territories and nest-sites are able to breed when supplemented with extra food or provided with mating partners. In vole-eating Tengmalm's owl, Aegolius funereus, we provided supplementary food and transferred females in nest-boxes of non-breeding males. Bachelor males that we supplemented with food did not attract mates at a higher frequency than unfed control males, which suggests that a lack of food did not influence the ability to attract a mating partner. In contrast, bachelor males presented with a female seemed to breed more frequently than bachelor males in the control group without mate addition. This suggests that scarcity of females may be an important reason for the high proportion of non-breeding males in the population (c. 25%) and excludes the possibility that non-breeding males are physiologically unable to breed. The operational sex ratio of the owl population at the time of mating may be male-biased, and some males may thus remain unpaired. Habitat and nest-box quality also seemed to be lower among bachelors than among breeding males. Received: 22 September 1997 / Accepted: 29 December 1997     

Experimental evidence that brighter males sire more extra‐pair young in tree swallows

Across taxa, extra‐pair mating is widespread among socially monogamous species, but few studies have identified male ornamental traits associated with extra‐pair mating success, and even fewer studies have experimentally manipulated male traits to determine whether they are related directly to paternity. As a consequence, there is little experimental evidence to support the widespread hypothesis that females choose more ornamented males as extra‐pair mates. Here, we conducted an experimental study of the relationship between male plumage colour and fertilization success in tree swallows (Tachycineta bicolor), which have one of the highest levels of extra‐pair mating in birds. In this study, we experimentally dulled the bright blue plumage on the back of males (with nontoxic ink markers) early in the breeding season prior to most mating. Compared with control males, dulled males sired fewer extra‐pair young, and, as a result, fewer young overall. Among untreated males, brighter blue males also sired more extra‐pair young, and in paired comparisons, extra‐pair sires had brighter blue plumage than the within‐pair male they cuckolded. These results, together with previous work on tree swallows, suggest that extra‐pair mating behaviour is driven by benefits to both males and females.     

Is only the first mating effective for females in the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)?

Although only the first mating is effective for females in Tetranychus urticae (Acari: Tetranychidae), it remains unclear whether this is also true for closely related species, such as T. kanzawai. To address this question, I analyzed paternity in the progeny of T. kanzawai females that had been observed to copulate with two males by using a microsatellite DNA marker. In this study, mating was allowed to take place without experimental interruption. The results show that progenies were sired by both males in only 1 of 14 families, whereas progeny were sired only by the first males in the other families. This result suggests that only the first mating would be, by and large, effective in T. kanzawai.     

Relatedness Does not Affect Competitive Behavior of Rival Males or Offspring Growth in Multiply Sired Litters of Bank Voles (Myodes glareolus)

Kin selection operates through the fitness of an organism's relatives. In the polyandry context, kin selection may be observable on the one hand in competition between rival males and, on the other hand, in competition between litter mates. Sperm competition theory predicts that males should invest less into mating when competing for fertilizations against a close relative as compared to an unrelated male. We tested this hypothesis with bank voles (Myodes glareolus) by mating each focal male to two females: one of which had previously mated with a full sibling of the focal male and the other one with a male unrelated to the focal male. However, we found no effect of rival male relatedness on mating behavior or proportion of offspring sired by the 2nd male to mate. Possibly, the probability of successive mating of related males with the same female is too low in natural bank vole populations for selection to have fine‐tuned mating behavior in relation to rival male relatedness. Further, polyandry often results in litters sired by multiple males. Litter mates of such litters have a reduced relatedness and are thus expected to be less cooperative during gestation and lactation, which may impair growth. Following double matings with either two full‐sibling males or two unrelated males, we compared offspring growth at birth and during lactation. Against our prediction, there was no difference in growth between litters sired either by two full‐sibling males or by two unrelated males. Either the conflict was not severe enough to be visible with our sample size (N = 16) or it may have been resolved by maternal control of offspring provisioning.     

Social Organization of North Island Brown Kiwi: Long-term Pairs and Three Types of Male Spacing Behaviour

We observed 51 kiwi by radiotracking for an average period of 2.3 months each, in Waitangi State Forest, New Zealand. Spacing data for more than one reproductive season are available from 27 individuals, with intervals of up to six years for some of them. Females have a high potential for polyandry, especially in the Waitangi population with a male-biased sex ratio of 1.4: 1. However, behavioural evidence suggests a monogamous mating system with long-term pair bonds. Pair members tend to stay close to each other and nearly all observed social interactions were between them. We show that there are three types of male spacing behaviour, which are related to the pairing status. A surplus of fully grown males (22.1% in 1986, 37.3% in 1987) remained unpaired. About half of these bachelor males maintained territories, which were twice the size of paired males' territories. This probably serves to recruit mates. The other half of unpaired males used huge home ranges of six times the size of paired males' territories, overlapping several territories of conspecifics. We have no evidence that these floaters take part in reproduction.     

Male mating strategies and the mating system of great-tailed grackles

Great-tailed grackles (Quiscalus mexicanus) are sexually dimorphic,dichromatic, colonially nesting blackbirds. In this study, males pursued three basic types of conditional mating strategies,each of which employed a different set of mating tactics. Territorialmales defended one or more trees in which several females nested.They achieved reproductive success by siring the offspringof their social mates and through extrapair fertilization.Resident males lived in the colony but did not defend territoriesor have social mates. Transient males passed through the colony, staying no more than a few days, and probably visited more thanone colony. Residents appeared to queue for access to territories,but transients did not. Residents and transients gained allpaternity through extrapair fertilizations and provided noparental care. Territorial males sired the majority of offspring,but residents and transients also sired small numbers of nestlings. Territorial males were larger and had longer tails than nonterritorialmales. The number of social mates was related to body size,and males that sired nestlings were heavier and had longertails than males with no genetic reproductive success. Malesthat gained paternity through extrapair fertilization wereheavier and had longer tails than males that did not. The matingsystem of great-tailed grackles can best be categorized as "non-faithful-female frank polygyny."     

Mate size and breeding success in a monogamous cichlid fish

Synopsis The patterns of mate size and parental care of a monogamous cichlid fish,Cichlasoma maculicauda, were studied in Gatun Lake, Panama. Males defend territories which serve as courtship and nest sites. Within a population most mates in pairs are of equal size rank. In each pair the male is larger than the female, probably because most mature males are larger than most mature females. Clutch size increases with female body size. Male size affects breeding success in two ways. First, larger males provide nest sites less susceptible to destructive wave action. Second, young of larger males grow faster than young of smaller males. Large males defeat small males in contests for position in feeding areas, and this may provide their young with better feeding conditions. In the laboratory young growth rates increase with food abundance, and at high levels of food surpass those observed in nature. Fast growth of young reduces their vulnerability to predators and should allow parents to breed more often. Young survival rates improve with the size of the parents, so that larger fish raise more offspring at each breeding attempt. These observations suggest why preference for large mates should occur.     

The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death

Male-biased dimorphism in body size is usually attributed tosexual selection acting on males, through either male competitionor female choice. Brown antechinuses (Antechinus stuartii) aresexually dimorphic in size, and heavier males are known to siremore offspring in the wild. We investigated four possible mechanismsthat might explain this large-male reproductive advantage. Wetested if there is a female preference for large males, a femalepreference for dominant males, if larger males compete moreeffectively for mates, and if there is a survival advantagefor large males during the mating season. We established nestinggroups of males in captivity and conducted mate choice trialsin which males from nesting groups either could or could notinteract. We assessed male dominance rank and recorded survivaltimes after mating. Females did not prefer larger males directly.The results suggest that the other three mechanisms of sexualselection tested account for the large-male advantage: largemales competed more successfully for mates, so were sociallydominant; females rejected subordinates (males they saw losingtwice in contests to previous mates); and dominant males survivedfor longer after their first mating. Females judged male rankbased on direct observation of male competitive interactionsat the time of mating and apparently could not distinguish rankfrom male scent. Effects of size and dominance on male reproductivesuccess are not confounded by age because male antechinusesare semelparous.     

Behavioural and genetic assessment of reproductive success in a spawning aggregation of the Australian giant cuttlefish, Sepia apama

The only known spawning aggregation of cuttlefish occurs in winter in southern Australia. The operational sex ratio in this aggregation is highly skewed towards males (range 11:1 to 4:1). Using SCUBA, we videotaped females as they mated with up to six males/h. Females rejected and accepted mates of any status or size. We obtained individual eggs and tissue samples from females and their mates and determined paternity by microsatellite DNA analysis. Thirty-nine eggs were sampled during 17 observational sequences (trials); 22 eggs were sired by a sampled male. One-third of the females mated with multiple males and 67% of females' eggs had multiple sires (N=9). Given our restricted sampling, these results probably underestimate actual levels of multiple paternity. Males competed to guard and copulate with females, and spent most of the copulation time flushing water into the female's buccal area. Thus, we predicted a high probability of fertilization of the next-laid egg(s) by the last male to mate, but this prediction was not statistically supported by our data. Fertilization success did not differ significantly between paired consorts (36%) and unpaired males (31%), or between large (33%) and small males (29%). Females used sperm from paired, unpaired and sneaker males as well as from previous matings to fertilize eggs. Our results indicate that this mating system has a high level of multiple mating and multiple paternity and that males of any size or status can obtain successful fertilizations.     

Host instar, body size and fitness in the koinobiotic parasitoid Aphidius nigripes

In aphidiine parasitoids, resources for growth and adult body size increase with host instar used by ovipositing females, but the fitness consequences of body size on fitness are poorly documented. We compared the fitness of male and female A. nigripesadults that varied in size as a consequence of developing in different instars of their host Macrosiphum euphorbiae. When reproductive fitness was measured without considering time, female wasps from small and large hosts performed similarly, contributing 125–175 foundresses plus 100–180 sons to the next generation. However, when expressed as the innate capacity for increase (r _m), female fitness correlated with host-induced variation of wasp size, indicating that micropopulations initiated by large wasps would increase faster. In a wind-tunnel, a sex pheromone plume from large female wasps induced more males to fly upwind when released at a distance of 50 cm downwind than small females, indicating that large females were sexually more attractive. With respect to male body size effects on fitness, large individuals performed similar to small ones, whether fitness was measured by lifetime mating frequency, fertile inseminations, or proportion of daughters among progeny born from their mates. When young naive males of unequal size were directly competing for mating with a virgin female, small and large males had equal mating success, and large individuals were no more successful than small ones at displacing a competitor already positioned on a receptive female. In a wind-tunnel test where males were scored on their ability to reach a female pheromone source, small and large males were equally affected by wind speed but reached the source located 50 cm downwind in equal proportions, suggesting similar capacity for finding mates by flying upwind. Our results indicate that despite host resources not being fixed at the time of attack for the koinobiont A. nigripes, fitness consequences of resource limitation by the mother may be perceived to be greater for daughters than sons, which would explain male-biased sex ratio in early-instar hosts.     

Insights into the mating habits of the tiger salamander (Ambystoma tigrinum tigrinum) as revealed by genetic parentage analyses

Among urodeles, ambystomatid salamanders are particularly amenable to genetic parentage analyses because they are explosive aggregate breeders that typically have large progeny arrays. Such analyses can lead to direct inferences about otherwise cryptic aspects of salamander natural history, including the rate of multiple mating, individual reproductive success, and the spatial distribution of clutches. In 2002, we collected eastern tiger salamander (Ambystoma tigrinum tigrinum) egg masses (> 1000 embryos) from a approximately 80 m linear transect in Indiana, USA. Embryos were genotyped at four variable microsatellite loci and the resulting progeny array data were used to reconstruct multilocus genotypes of the parental dams and sires for each egg mass. UPGMA analysis of genetic distances among embryos resolved four instances of egg mass admixture, where two or more females had oviposited at exactly the same site resulting in the mixing of independent cohorts. In total, 41 discrete egg masses were available for parentage analyses. Twenty-three egg masses (56%) consisted exclusively of full-siblings (i.e. were singly sired) and 18 (44%) were multiply sired (mean 2.6 males/clutch). Parentage could be genetically assigned to one of 17 distinct parent pairs involving at least 15 females and 14 different males. Reproductive skew was evident among males who sired multiply sired clutches. Additional evidence of the effects of sexual selection on male reproductive success was apparent via significant positive correlations between male mating and reproductive success. Females frequently partitioned their clutches into multiple discrete egg masses that were separated from one another by as many as 43 m. Collectively, these data provide the first direct evidence for polygynandry in a wild population of tiger salamanders.     

The mating chances of small males of the cerambycid beetleTrachyderes mandibularis differ in different environments (Coleoptera: Cerambycidae)

Some males of the cerambycid beetle Trachyderes (Dendrobias) mandibularisgained access to mates by defending a patchily distributed food resource, the fruits of saguaro cactus (Cereus giganteus).Male beetles differed greatly in fighting ability because of extreme variation in body size and a striking dimorphism in mandibular weaponry. As is typical in resource defense mating systems, larger males had an advantage in combat. Major males with their large pincer jaws invariably defeated minor males with small cutting jaws, and larger majors usually defeated smaller majors. However, although minor males were at a competitive disadvantage on saguaro fruits, they did not suffer a great penalty in terms of mating probability. In contrast, minor males have a considerably lower probability of mating at desert broom (Baccharis sarothroides)where sap ooze sites are few in number and effectively monopolized by major males (Goldsmith, S. K., Behav. Ecol. Sociobiol.20,111–115, 1987). On saguaros, minor males successfully obtained mates through scramble competition while avoiding direct physical competition with larger, territorial major males. Smaller males of either morph may have succeeded in acquiring mates in part because there were many more ripe saguaro fruits than beetles, which made it impossible for larger major males to monopolize females effectively under these conditions.     

A genetic analysis of body size in pink salmon (Oncorhynchus gorbuscha)

Two small-sized and two large-sized male pink salmon (Oncorhynchus gorbuscha) were mated to each of four females, producing eight families sired by small males and eight sired by large males. The juveniles were reared for 500 d after fry emergence. Juvenile weight in the two male size classes was similar until the spring of the year of maturity, when juveniles sired by large males grew faster than those sired by small ones. Heritability estimates of weight based upon the dam component of variance increased during 500 d of rearing from 0.4 to 0.8. Heritability of weight based upon the sire component of variance generally ranged between 0.1 and 0.3. The large variation in male body size in spawning pink salmon populations may have resulted from different male breeding strategies.     

Habitat fragmentation reduces plant progeny quality: a global synthesis

Most of the world's land surface is currently under human use and natural habitats remain as fragmented samples of the original landscapes. Measuring the quality of plant progeny sired in these pervasive environments represents a fundamental endeavour for predicting the evolutionary potential of plant populations remaining in fragmented habitats and thus their ability to adapt to changing environments. By means of hierarchical and phylogenetically independent meta‐analyses we reviewed habitat fragmentation effects on the genetic and biological characteristics of progenies across 179 plant species. Progeny sired in fragmented habitats showed overall genetic erosion in contrast with progeny sired in continuous habitats, with the exception of plants pollinated by vertebrates. Similarly, plant progeny in fragmented habitats showed reduced germination, survival and growth. Habitat fragmentation had stronger negative effects on the progeny vigour of outcrossing‐ than mixed‐mating plant species, except for vertebrate‐pollinated species. Finally, we observed that increased inbreeding coefficients due to fragmentation correlated negatively with progeny vigour. Our findings reveal a gloomy future for angiosperms remaining in fragmented habitats as fewer sired progeny of lower quality may decrease recruitment of plant populations, thereby increasing their probability of extinction.     

Paternal effects on offspring traits in Scaphiopus couchi (Anura: Pelobatidae)

Summary Maternal half-siblings sired by large male Scaphiopus couchi had higher probabilities of surviving than maternal half-sibs sired by smaller males. Half-sibs sired by large and small males did not differ in tadpole body weight, duration of larval period, number of toadlets produced, or toadlet body weight. These results suggest that which male a female mates with may influence important components of her offspring's fitness.     

Measuring polyandry in wild populations: a case study using promiscuous crickets

Mating rate has important implications for patterns of sexual selection and sexual conflict and hence for issues such as speciation and the maintenance of genetic diversity. Knowledge of natural mating rates can provide insights into the factors driving female mating behaviour. We investigated the level of polyandry in a Spanish population of the field cricket Gryllus bimaculatus using microsatellite markers. Two approaches were employed: (i) genotyping the offspring of wild-caught gravid females to determine the number of males siring the brood and (ii) genotyping sperm stored in the spermathecae of females mated in the wild to estimate the number of mating partners. We compared existing methods for inferring the minimum and probable number of fathers and described a novel probabilistic technique estimating the number of mates by genotyping stored sperm. Using the most conservative allele-counting method, 71% of females produced offspring sired by at least two males (a minimum mean of 2.4 fathers per clutch), and all females had mated to at least two males with minimum mean estimates of 2.7-5.1 mates per female. Our study reveals high levels of polyandry in the wild and suggests that females mate with more males than sire their offspring.     

Increase in numbers of male fur seals Arctocephalus gazella during the summer autumn period at Mossman Peninsula (Laurie Island)

Summary The fur seal, Arctocephalus gazella, population at Mossman Peninsula (Laurie Island) was studied from 1985 to 1987. Weekly counts were carried out at a 4 km bachelor haul-out beach from December through June. Maxima of 2 240, 2 787 and 5 196 juvenile and adult males were counted during March of the respective years. Census data indicate an increase in the non-breeding population of 13.5% between 1985–1986 and 46.5% between 1986–1987.     

Genetic life history effects on juvenile survival in bluegill

Foraging behaviour under the risk of predation has important consequences on an individual's survivorship and fitness. In bluegill (Lepomis macrochirus), we have recently shown that offspring sired by males of alternative life histories differ in their foraging behaviour. Specifically, offspring sired by 'cuckolder' males take fewer risks during foraging than do offspring sired by 'parental' males. This behavioural difference can have important consequences on the fitness of the two life histories and thus the underlying evolutionary mechanism. Here, we examine the consequences of this behavioural variation on growth rate, condition and survivorship during early development of juveniles. We used split in vitro fertilization to generate maternal half-sibs that differed in sire life history. The resulting 18 455 larvae from 50 families were released into a microcosm with safe and risky foraging areas for approximately 2 months. A total of 262 juveniles (1.4%) survived of which parentage was unambiguously determined using microsatellite genetic markers for 254 (97%). Although we found significant dam effects, there was no difference in apparent growth rate or condition of juveniles sired by males of the two life histories. Of the 25 paired half-sib families, 15 had higher survivorship when sired by a cuckolder male, seven had higher survivorship when sired by a parental male and three had no surviving offspring from either sire. Thus, although growth was similar between the two offspring types, survivorship was not. Combining the differential survivorship estimate with paternity data from natural nests and the frequency of males adopting each life history, we calculated that the cuckolder life history has 1.87 times higher fitness than the parental life history. As such, the life histories likely are not governed by a genetic polymorphism.