Do individuals in better condition survive for longer? Field survival estimates according to male alternative reproductive tactics and sex

There is a gap in terms of the supposed survival differences recorded in the field according to individual condition. This is partly due to our inability to assess survival in the wild. Here we applied modern statistical techniques to field‐gathered data in two damselfly species whose males practice alternative reproductive tactics (ARTs) and whose indicators of condition in both sexes are known. In Paraphlebia zoe, there are two ART: a larger black‐winged (BW) male which defends mating territories and a smaller hyaline‐winged (HW) male that usually acts as a satellite. In this species, condition in both morphs is correlated with body size. In Calopteryx haemorrhoidalis, males follow tactics according to their condition with males in better condition practicing a territorial ART. In addition, in this species, condition correlates positively with wing pigmentation in both sexes. Our prediction for both species was that males practicing the territorial tactic will survive less longer than males using a nonterritorial tactic, and larger or more pigmented animals will survive for longer. In P. zoe, BW males survived less than females but did not differ from HW males, and not necessarily larger individuals survived for longer. In fact, size affected survival but only when group identity was analysed, showing a positive relationship in females and a slightly negative relationship in both male morphs. For C. haemorrhoidalis, survival was larger for more pigmented males and females, but size was not a good survival predictor. Our results partially confirm assumptions based on the maintenance of ARTs. Our results also indicate that female pigmentation, correlates with a fitness component – survival – as proposed by recent sexual selection ideas applied to females.     

Male dimorphism, territoriality and mating success in the tropical damselfly, Paraphlebia zoe Selys (Odonata: Megapodagrionidae)

The tropical damselfly Paraphlebia zoe has two male morphs: a black-winged (BW) male which is associated with territorial defense of oviposition sites; and a hyaline-winged (HW) male similar in appearance to females, and, compared to the black morph, less frequently found defending territories. In a wild population of this species, we first assessed the relationship between phenotypic traits [male morph, size and territorial status (being territorial or non-territorial)], their role on mating success, and the degree to which a particular territory may contribute to male mating success. Second, to relate a physiological basis of being territorial we compared both morphs in terms of muscular fat reserves and thoracic muscle, two key traits related to territory defense ability. Males of both morphs defended territories although the BW males were more commonly found doing this. BW males were larger than HW males and size predicted being territorial but only within HW males (territorial males were larger) but not in BW males. Male mating success was related to territorial status (territorial males achieved a higher mating success), but not to morph or size. Furthermore, territory identity also explained mating success with some territories producing more matings than others. The BW morph stored more fat reserves which may explain why this morph was more likely to secure and defend a place than the HW morph. However, the HW morph showed higher relative muscle mass which we have interpreted as a flexible strategy to enable males to defend a territory. These results are distant to what has been found in another male dimorphic damselfly, Mnais pruinosa, where the advantage of the non-territorial morph relies on its longevity to compensate in mating benefits compared to the territorial morph.     

Alternative reproductive tactics are associated with sperm performance in invasive round goby from two different salinity environments

During male–male competition, evolution can favor alternative reproductive tactics. This often results in a dominant morph that holds a resource, such as a nest for egg laying, which competes with a smaller sneaker morph that reproduces by stealing fertilizations. The salinity environment can influence male growth rates, for example, via osmoregulatory costs, which in turn may influence the use of sneaker tactics for small males competing for mating opportunities. Salinity can also affect sperm directly; however, little is known of how salinity influences sneaker tactics through sperm performance. We sampled males of the invasive round goby (Neogobius melanostomus) from two environments, a freshwater river and a brackish estuary. This fish has two male morphs: nest‐holding dark males and non‐nest‐holding light males. We examined the role of water salinity of 0, 8, and 16 on sperm performance and found that for estuarine males, a salinity of 0 reduced sperm velocity compared to a salinity of 8 and 16. Riverine males had low velocity in all salinities. Sperm viability also decreased by over 30% in 0 salinity, compared to 8 and 16, for fish from both environments. Gobies produce ejaculate contents in specialized glands that could in theory shield sperm in an adverse environment. However, gland contents did not improve sperm performance in our tests. Body mass and age estimates indicate that riverine males invested more in somatic growth compared to estuarine males. Estuarine light morph males had a high enough gonadosomatic index to indicate sneaker tactics. We propose that when sperm performance is low, such as for the riverine males, sneaker tactics are ineffective and will be selected against or phenotypically suppressed. Instead, we interpret the increased investment in somatic growth found in riverine males as a life‐history decision that is advantageous when defending a nest in the next reproductive season.     

Mating tactics and male wing dimorphism in the damselfly,Mnais pruinosa costalis selys (Odonata: Calopterygidae)

Males of the damselfly,Mnais pruinosa costalis, exhibit wing color dimorphism: one form has orange wings, and the other hyaline wings which resemble female wings. The former is usually territorial and the latter uses sneaky mate securing tactics. When orange-winged males failed to establish territory, they became floaters that day. Hyaline-winged males perched around their territories and often, formed in tandem without any apparent courtship behavior when they found females. Their copulation frequency was higher and copulation duration longer than those of territorial males. A few females oviposited without remating. Total oviposition duration of females with which a hyaline-winged male mated was more than 32 min per male on average in a day Females that copulated with hyaline-winged males often remated with orange-winged residents before oviposition. Total duration of oviposition bouts of females after mating with floaters was short (15 min), while that with territorial residents was long (66 min). As a result, total oviposition duration of females with which an orange-winged male mated was about 40 min in a day. The reproductive success of the hyaline-winged males may be similar to that of the orange-winged males.     

Phenotypic variation between dimorphic males in corkwing wrasse

The age-frequency distributions for sneaker males (individuals with female secondary sexual characters) and territorial males (individuals with typical male sexual characters) of corkwing wrasse Symphodus melops in a Swedish population did not differ. Otolith analysis revealed that sneaker males were smaller than their territorial male counterparts as juveniles, but there was no evidence of a clear-cut threshold to determine the subsequent reproductive patterns. Thus, the expression of male morph in corkwing wrasse most likely is related to early growth pattern and the different morphs could be fixed for life. Adult sneaker males in general were smaller than territorial males of the same age. The relative gonad size and the abdomen in sneaker males were substantially enlarged compared with territorial males, but there was no difference in gonad water content between the two types of males. Sneaker males weighed less in relation to their length than territorial males. These results support theoretical sperm competition models which predict that the male morph with reduced attractiveness to females (i.e. sneakers) should invest more into spermatogenesis in order to achieve fertilization than the attractive male morph (i.e. territorial males).     

Time constraints related to sexual maturation and prolonged copulation in the female‐dimorphic damselfly Ischnura senegalensis

Time constraints are critical for reproductive success. To understand the spatiotemporal dynamics of morph frequency in the female‐dimorphic damselfly Ischnura senegalensis, we compared two different morphs for two important time constraints on female reproductive output, i.e. post‐emergence sexual maturation and prolonged copulation. The females of both morphs achieved sexual maturation 4–5 days after emergence, suggesting that the rate of sexual mutation does not result in morph‐specific fitness. The copulation durations declined with the time of onset of copulation in both morphs. Consequently, all copulations terminated at approximately 12:00 hours. Because females show foraging and oviposition activity only after copulation, the copulation duration does not result in morph‐specific time constraints. These two important time constraints do not account for morph‐specific reproductive success and do not affect the evolutionary equilibrium of morph frequency in I. senegalensis.     

Body Size and Multiple Copulations in a Neotropical Grasshopper with an Extraordinary Mate-Guarding Duration

After copulation, male grasshoppers of Sphenarium purpurascens (Orthoptera: Pyrgomorphidae) remain in a postinsemination association with their mate. A male can spend as many as 17 days mounted on a female. Guarding duration is related to both male and female body size and the female's mating history. Longest guarding durations were recorded at the middle of the reproductive season, when the probability of encounter between the sexes (sex ratio and population density) was decreasing, at the beginning of the associated dry season. These guardings were associated with large individuals of both sexes and with females that had more previous partners. Moreover, a positive association was found among guarding duration, female and male body size and age, and number of copulations performed by the males. Maybe males invest time and sperm in females as a function of the probability of sperm competition. Nevertheless, guarding may provide benefits to both sexes. Males may reduce the possibility of sperm competition, and females may obtain nutritional benefit for themselves or their offspring as a result of multiple copulations. Changes in male investment in guarding duration and number of copulations may be the result of physiological constraints related to seminal and/or sperm production. Moreover, guarding duration could be constrained by ecological factors such as a reduction of food availability associated with the beginning of the dry season.     

Patterns of Sperm Transfer in the Golden Orb‐Weaver Nephila edulis

Sperm competition studies typically identify copulation duration as an important predictor of paternity as it may determine the quantity of sperm transferred and thus paternity success. This study explores the relationship between copulation duration, male body size, male age and sperm transfer in the golden orb‐weaving spider, Nephila edulis. Paternity in this species is strongly associated with the relative frequency and duration of copulation, which is also influenced by male size. We determined the number of sperm transferred during copulation, by performing sperm counts in both the male copulatory organs (palps) and female sperm receptacle (spermatheca) of recently mated pairs. The total number of sperm recorded (the sum in the male palps and female spermathecae) was greater for younger males than older males, but did not vary with male body size. In general, younger males transferred more sperm and a greater proportion of their sperm supplies than older males and, among these younger males, larger individuals transferred more sperm. However, there were no significant size effects for older males. More sperm was transferred with longer copulations, but in contrast with previous studies, we found that larger males copulated for longer. The rate of sperm transferred was negatively correlated with the duration of copulation, suggesting that the variation in copulation duration in N. edulis may represent strategic investment by males to alter patterns of paternity, in addition to transferring additional sperm.     

Operational Sex Ratio and Alternative Reproductive Behaviours in Chinese Bushcricket, Gampsocleis gratiosa

The effects of operational sex ratio (OSR) on male mating tactics in the Chinese bushcricket Gampsocleis gratiosa were investigated in male‐ and female‐biased environments. We measured fresh and dry spermatophore contents and copulation duration, and counted sperm numbers of each copulation. The fresh weight of spermatophore and spermatophylax was positively correlated with male body weight. The males in a strongly male‐biased environment produced significantly heavier fresh ampulla and more sperm per ejaculation, which were likely tactics for successful matings under the competition of rivals. The spermatophore might function as a structure to protect the fertilization potential of the ejaculate from rival males.     

The prediapause copulation and its significance in the butterflyEurema hecabe

In the pierid butterflyEurema hecabe, which shows seasonal polymorphism (summer and autumn morphs) and overwinters at adult stage, whether or not the prediapause copulation may be of usual occurrence and reproductively functional was examined. From the counts of the spermatophores carried by the females, it is clear that the prediapause copulation characteristically occurs in reproductively inactive females of the autumn corph. From behavioral observations in the field, mating partners of those females are mostly males of the summer morph rather than from the autumn morph. In autumn, males of the summer morph remained abundant and searched for females on the larval food plants. Furthermore, they mated frequently with autumn morph females. Autumn morph males seemed to be sexually less active or inactive before hibernation. Microscopic examinations of the spermathecae were made in mated autumn-morph females collected before and after hibernation. The results indicate that sperm is passed by the males at autumnal copulation. The sperm may be stored in the female reproductive tract and utilized for fertilization in spring. This supposition is strongly supported by field data; that is, once-mated autumn-morph females laid fertilized eggs in spring. Finally, physiological basis of the prediapause copulation, its adaptive signficance and the behavioral advantage inE. hecabe are discussed from the viewpoint of seasonal adaptation.     

Description of alternative male reproductive tactics in a shell-brooding cichlid, Telmatochromis vittatus, in Lake Tanganyika

Telmatochromis vittatus (Cichlidae) is a Tanganyikan substrate brooder which spawns in the gastropod-shell nests of a cichlid, Lamprologus callipterus. We describe male reproductive tactics of T. vittatus in and around the shell nests, where males of various sizes were found. Based on utilization patterns of the shell nests, interactions among males, and spawning behaviors, males could be categorized into four types based on reproductive tactics and in order of body size: sneaker males, satellite males, territorial males and piracy males. Size range of males in tactic groups rarely overlapped. Territorial males defended shell nests harboring multiple females, but during pair-spawning they were occasionally taken over by large piracy males that visited several nests repeatedly. Small sneaker males darted to pair-spawning territorial males and might ejaculate sperm. Satellite males did not perform parasitic spawning but pair-spawned in a single shell outside the nests. Spawning of satellite males was infrequently parasitized. The largest gonado-somatic index (GSI) was found in sneaker males followed by piracy males, territorial males and satellite males, suggesting that gonadal investment of males using the four tactics may be consistent with intensity or risk of sperm competition.     

An experimental investigation into status-dependent male dimorphism in the European earwig, Forficula auricularia

Discrete alternative reproductive phenotypes are probably often due to individuals adopting alternative tactics with unequal fitnesses in conditional strategies with status-dependent selection. One tactic is believed to be favoured below a status switch point and another tactic above it, owing to different fitness functions of the tactics. Males of the European earwig are dimorphic. Macrolabic males are large (high status) and have long forceps, and brachylabic males are small (low status) with short forceps. I tested whether fitness functions, measured as mating success, of the two morphs differed with regard to forceps length and body weight. Macrolabic males with longer forceps than a competing male had higher mating success but brachylabic males benefited by being heavier than their competitor. Thus, different selection regimes were acting on the two morphs, suggesting that their fitness functions differed in relation to status. These observations and those of previous studies, showing that morph expression is environmentally determined and is associated with body size and that the morphs have unequal fitness, provide support for the hypothesis that male dimorphism in this species is a conditional strategy that has evolved under status-dependent selection. The differential investment in forceps growth that characterizes the morphs was manifested in a steeper allometric relation between forceps length and body size in macrolabic than brachylabic males. Behavioural observations showed that males of both morphs engaged in direct contests for females. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Sperm competition and small size advantage for males of the golden orb‐web spider Nephila edulis

Sexual selection, through female choice and/or male–male competition, has influenced the nature and direction of sexual size dimorphism in numerous species. However, few studies have examined the influence of sperm competition on size dimorphism. The orb‐web spider Nephila edulis has a polygamous mating system and extreme size dimorphism. Additionally, the frequency distribution of male body size is extremely skewed with most males being small and few large. The duration of copulation, male size and sexual cannibalism have been identified as the significant factors determining patterns of sperm precedence in spiders. In double mating trials, females were assigned to three treatments: either they mated once with both males or the first or the second male was allowed to mate twice. Paternity was strongly associated with the duration of copulation, independent of mating order. Males that were allowed to mate twice not only doubled the duration of copulation but also their paternity. Small males had a clear mating advantage, they copulated longer than large males and fertilized more eggs. Males of different sizes used different tactics to mate. Large males were more likely to mate through a hole they cut into the web, whereas small males approached the female directly. Furthermore, small males usually mated at their first attempt but large males required several attempts before mating took place. There was no obvious female reaction towards males of different sizes.     

Impact of cryptic female choice on insemination success: Larger sized and longer copulating male squid ejaculate more,but females influence insemination success by removing spermatangia

In polyandrous mating systems, sperm competition and cryptic female choice (CFC) are well recognized as postcopulatory evolutionary forces. However, it remains challenging to separate CFC from sperm competition and to estimate how much CFC influences insemination success because those processes usually occur inside the female's body. The Japanese pygmy squid, Idiosepius paradoxus, is an ideal species in which to separate CFC from sperm competition because sperm transfer by the male and sperm displacement by the female can be observed directly at an external location on the female's body. Here, we counted the number of spermatangia transferred to, removed from, and remaining on the female body during single copulation episodes. We measured behavioral and morphological characteristics of the male, such as duration of copulation and body size. Although males with larger body size and longer copulation time were capable of transferring larger amounts of sperm, females preferentially eliminated sperm from males with larger body size and shorter copulation time by spermatangia removal; thus, CFC could attenuate sperm precedence by larger males, whereas it reinforces sperm precedence by males with longer copulation time. Genetic paternity analysis revealed that fertilisation success for each male was correlated with remaining sperm volume that is adjusted by females after copulation.     

Dimorphic Males Display Alternative Reproductive Strategies in the Marine Amphipod Jassa marmorata Holmes (Corophioidea: Ischyroceridae)

Discrete dimorphism of males within a species is often the result of selection for alternative reproductive strategies, and these strategies may be evolutionarily stable (ESS). An ESS may be either mixed (genetically fixed differences) or conditional (flexible differences related to varying environmental conditions) (PARKER 1984). Mature males of the marine amphipod Jassa marmorata are dimorphic. Large ‘major’ males have a greatly enlarged thumb (propodus) on their 2nd gnathopods, while small ‘minor’ males exhibit thumbs that are reduced, and CONIAN (1989) suggested that minors may exhibit a different mating strategy from majors. Ratios of males and females fluctuate seasonally (FRANZ 1989) and female body size is inversely correlated with temperature (FRANZ 1989) so male dimorphism could be a flexible response to varying environmental conditions. I sampled a natural population of J. marmorata over a 1-yr period, quantified major and minor morphology, and measured male behaviour and mating success in experimental arenas that contained varying proportions of male morphs and females. Morphology of the two morphs is discrete; female body size varies with season with significantly smaller individuals in summer and fall; body size predicts morph type; and ratios of majors, minors and females fluctuate seasonally. Finally I showed that majors and minors use different mating tactics to gain access to receptive females, and that these behaviours depend on the male's own morphology and on the environmental setting that it finds itself in. Major males fight, display and attempt to evict other males to mate with receptive females. Minors never fight with, display to or attempt to evict majors, but they infrequently display to and attempt to evict other minor males. Furthermore, mating success of the two morphs was not significantly different and may depend on whether males are with a majority or minority of their own type. These data support the conclusion that major and minor male J. marmorata display evolutionarily stable alternative reproductive strategics, but more work should address the nature of this ESS.     

Body Size Correlates with Fertilization Success but not Gonad Size in Grass Goby Territorial Males

In fish species with alternative male mating tactics, sperm competition typically occurs when small males that are unsuccessful in direct contests steal fertilization opportunities from large dominant males. In the grass goby Zosterisessor ophiocephalus, large territorial males defend and court females from nest sites, while small sneaker males obtain matings by sneaking into nests. Parentage assignment of 688 eggs from 8 different nests sampled in the 2003–2004 breeding season revealed a high level of sperm competition. Fertilization success of territorial males was very high but in all nests sneakers also contributed to the progeny. In territorial males, fertilization success correlated positively with male body size. Gonadal investment was explored in a sample of 126 grass gobies collected during the period 1995–1996 in the same area (61 territorial males and 65 sneakers). Correlation between body weight and testis weight was positive and significant for sneaker males, while correlation was virtually equal to zero in territorial males. That body size in territorial males is correlated with fertilization success but not gonad size suggests that males allocate much more energy into growth and relatively little into sperm production once the needed size to become territorial is attained. The increased paternity of larger territorial males might be due to a more effective defense of the nest in comparison with smaller territorial males.     

The relative costs and benefits of territorial defense and the two conditional male mating tactics in the Comanche Springs pupfish (Cyprinodon elegans)

We examined the aggressive costs and reproductive benefits of territorial defense and its alternatives in a population of the Comanche Springs pupfish (Cyprinodon elegans). The breeding system was characterized by three different male mating tactics: territorial defense, satellite positioning, and sneak spawning. The mating tactic adopted by males reflected the males' sizes. Territorial residents were the largest, satellites were medium-sized, and sneakers were the smallest adult males observed. Consistent with the hypothesis that primary mating tactics are relatively high-cost, high-benefit strategies, we found that territorial males engaged in a number of aggressive encounters but had higher reproductive successes than any other males. However, our observations did not support the premise that conditionally breeding males engage in relatively low-benefit, low-cost tactics. Medium satellites and small sneakers acquired fewer spawns than did territorial males, but both satellites and sneakers were involved in as much aggression as territorials. That is, the data supported the prediction that satellite or sneaker males with the inability to compete for territories would attempt to accrue some reproductive opportunities in the presence of territorial males despite the high costs of spending time on the breeding grounds. Adopting conditional tactics appeared to allow satellites and sneakers to make the best of a bad situation. During a subsequent breeding season, large males were absent from the population, and medium-sized males established territories. The aggressive behavior exhibited by medium residents was similar to the previous year, but these males did not acquire higher reproductive successes than medium satellites had. The implications of switching tactics and the influence of operational sex ratios on the costs and benefits of the male tactics are briefly addressed. Electronic Publication     

Male mate choice in the chameleon grasshopper (Kosciuscola tristis)

In many species, males can increase their fitness by mating with the highest quality females. Female quality can be indicated by cues, such as body size, age and mating status. In the alpine grasshopper Kosciuscola tristis, males can be found riding on subadult females early in the season, and as the season progresses, males engage in fights over ovipositing females. These observations suggest that males may be competing for females that are either unmated (early season) or sperm‐depleted (late season). We thus hypothesised that male K. tristis may be choosy in relation to female mating status, and specifically, we predicted that males prefer females that are unmated. We conducted behavioural experiments in which males were given the choice of two females, one mated and one unmated. Contrary to our prediction, males did not mate preferentially with unmated females. However, copulation duration with unmated females was, on average, 24 times the length of copulation with mated females. While female K. tristis can reject mates, we did not observe any evidence of overt female choice during our trials. Females may gain additional benefits from mating multiply and may therefore not readily reject males. While our experiment cannot definitively disentangle female from male control over copulation duration, we suggest that males choose to invest more time in copula with unmated females, perhaps for paternity assurance, and that male mate assessment occurs during copulation rather than beforehand.     

Variation in plasma steroids and reproductive traits in dimorphic males of corkwing wrasse (Symphodus melops L.)

Differences in plasma steroid levels may reflect behavioral, gonadal, or morphological specializations that characterize different male reproductive phenotypes in teleost fishes. In the present study, we investigated whether differences in plasma steroid levels exist between two distinct male morphs shown in the corkwing wrasse Symphodus melops. In addition, we examined differences in male reproductive traits, including gonad mass, sperm motility, and sperm concentration, between the two male types. Possible associations between plasma steroid levels and reproductive traits were also investigated. The results indicated that males with typical male secondary sexual characters (territorial males) had higher plasma levels of 11-ketotestosterone (11kT) compared to smaller males with female secondary sexual characters (female mimics). The female mimics in turn had higher plasma levels of both testosterone (T) and 17beta-estradiol. In addition, female mimics had relatively larger gonads and longer-lived sperm than territorial males. Relative gonad mass covaried significantly with the plasma levels of 11kT and T among the morphs, indicating that the relative gonad size correlates positively with the plasma level of these two steroids. However, there was no significant covariance between sperm traits and plasma steroids for the two male morphs. Hence, our results do not indicate any causal link between sperm quality and hormones.