Effect of sperm depletion and starvation on female mating behavior in the water strider,Aquarius remigis

The resolution of intersexual conflict over mating should be dependent on the current state of each individual. In this study, I used a factorial design to examine the influence of two physiological factors, sperm depletion and food deprivation, on resistance to mating by females of the water strider, Aquarius remigis. Females employ several different mate-resisting tactics during an encounter with a male. Five measures of female resistance to mating were identified: jumping, rolling, dunking, time spent dunking, and struggle duration. Jump, roll, and dunk rates were highly correlated with each other and combined into one metric of resistance to mating (PC1) using principal components analysis. Time per dunk (T/D) and struggle duration were also analyzed. Discrete male behaviors during the struggle could not be identified. Two measures of female resistance, PC1 and T/D, were significantly lower in sperm-depleted females than in sperm-replenished females. Struggle duration did not differ between the two treatments. Starvation had no effect on any of the measures of resistance. Sperm depletion significantly enhanced the probability of mating (54% vs. 24% for replenished females), while starvation had no effect on the probability of mating. I pooled all the females and compared females that mated with those that did not mate. Nonmating females resisted significantly more than mating females in all three measures of resistance. Path analysis indicated that PC1 was the only measure of resistance that was significantly negatively related to the probability of mating. Almost half (46%) of sperm-depleted females showed no resistance to males, while only 3% of sperm-replenished females were nonresistant. When nonresisters were removed from the analysis, sperm depletion had no effect on any of the measures of female resistance to mating and no effect on the probability of mating. In A. remigis, female resistance appears to be a yes/no phenomenon with respect to sperm depletion and not affected directly by starvation. Received: 2 September 1994/Accepted after revision: 9 September 1995     

Predation risk,food deprivation and non-random mating by size in the stream water strider,Aquarius remigis

Summary Non-random mating by size (NRMS) plays a central role in the study of sexual selection and the evolution of mating systems. Theory suggests that NRMS should be influenced by conflicting demands (e.g., predation risk, hunger); few experimental studies, however, have addressed these effects. We used a factorial experiment to examine the influence of predatory green sunfish and food deprivation on NRMS in male and female stream water striders, Aquarius remigis. As predicted by theory, food deprivation decreased the large-male mating advantage. The influence of predation risk, however, went against existing theory; that is, risk increased the large male mating advantage. The degree of large-male mating advantage was negatively related to a measure of the rate of male harassment of females. A behavioral mechanism that can explain these patterns emphasizes the contrasting effects of different competing demands on male harassment rates, female resistance and the role of male size in overcoming female resistance. Females usually resist male mating attempts. Successful mating occurs when males overcome female resistance. If harassment rates (of females by males) are low, larger males have a mating advantage over smaller males perhaps because females resist heavily and thus only larger males can overcome female resistance. If, however, male harassment rates are very high, female resistance might be swamped; mating should then be more random with respect to male size. Food deprivation increases gerrid activity and thus increases harassment rates which should then reduce NRMS. In contrast, risk decreases gerrid activity, thus decreasing harassment rates and increasing NRMS. Females did not show significant NRMS. Females did, however, show a pattern of change in NRMS that is consistent with male choice for larger females. Correspondence to: A. Sih     

Polyandry, multiple mating, and female fitness in a water strider Aquarius paludum

Contrary to Bateman’s principle, polyandry appears to be a common female mating strategy. Several hypotheses have been proposed to explain the evolution of polyandry. It is assumed that females gain either material or genetic benefits from multiple matings, or that they are coerced into mating by males. In water striders, mating is generally assumed to be costly to females, and they are thought to mate for reasons of convenience, adjusting their resistance to mating according to male harassment. Here, we tested the effect of number of matings (with the same male) and number of partners on female fitness in a water strider Aquarius paludum. In the first experiment, we regulated the time females spent with a male and found that females’ egg production increased with multiple matings up to a point. The result supports the existence of an optimal female mating frequency. In the second experiment, we tested how polyandry affects the number of eggs laid and egg hatching success. We conducted three different trials: females mated four times with either a single male, two different males, or with four different males. Females that mated with four different males laid the lowest number of eggs and had the lowest egg hatching success, suggesting that polyandry reduces females’ egg production and egg hatching success in A. paludum. We conclude that A. paludum females probably gain material benefits from mating but no genetic benefits were found in this study.     

Food threshold territoriality in a water strider (Gerris remigis)

Summary Summer generation 3rd, 4th and 5th instar nymphs plus adults of Gerris remigis were satiated for 2 days in a laboratory tray then deprived of food. Within 1/2–2 days, 19 of 27 nymphs and 10 of 30 adults began to exhibit territoriality, continued being so for 3–9 days, then ceased shortly before becoming quiescent. In the field, muscid flies fed to different territorial striders at a rate of 0, 1, 2, or 3 flies/day, resulted in 8 of 10 striders (at 2 flies/day) and 10 of 10 striders (at 3 flies/day) ceasing territoriality, whereas 5 of 8 controls (at 0 flies/day) remained territorial. Thus, lower and upper food thresholds were demonstrated, the upper threshold approached both from above (laboratory study) and below (field study).     

Alternative mating strategies in the water strider Gerris elongatus (Heteroptera,Gerridae)

Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution.     

The effects of operational sex ratio and food deprivation on copulation duration in the water strider (Gerris remigis Say)

Summary A North American water strider, Gerris remigis (Hemiptera) copulates for prolonged periods of time, apparently beyond the time necessary for insemination (Rubenstein 1984; Wilcox 1984; Clark 1987), I tested predictions from two different hypotheses of the adaptive significance of this behavior. Manipulations of the operational sex ratio in artificial streams revealed that water striders copulate significantly longer when the sex ratio is male-biased. This result is consistent with the hypothesis that prolonged copulation functions as a type of contact mate guarding, which reduces sperm competition by preventing the female from remating prior to oviposition. The finding is also consistent with the hypothesis that copulation is prolonged to enhance female foraging efficiency. In a second experiment, sex ratio and total population density were held constant, and the period of food deprivation of females was manipulated. Contrary to the predictions of the female foraging hypothesis, starved females did not copulate longer than fed females. Of the two hypotheses considered, only the copulatory guarding hypothesis explains both results. This does not mean, however, that there is no selective benefit from the enhanced foraging efficiency resulting from prolonged copulation. Nor does it exclude the possibility that this benefit has been necessary for the evolution of prolonged copulation in water striders.     

Experimental studies on water strider mating dynamics: spatial variation in density and sex ratio

Summary We used field surveys, field experiments and experiments in artificial pools to study the effects of variation in sex ratio and density on mating dynamics of a stream water strider, Aquarius remigis. Our field survey documented the existence of hot spots, sites of higher than average total gerrid density, a male-biased sex ratio, and higher than average female mating activity. Female gerrids frequently changed sites, usually moving upstream, perhaps to spread their eggs among many sites. Male gerrids showed two movement strategies: some males frequently changed sites, while other males were stationary at hot spots. Surprisingly, smaller males tended to be stationary at hot spots. A field manipulation of the availability of refuges for females to avoid harassment by males supported the notion that males prefer hot spots because they are sites where a scarcity of refuge for females makes it relatively easy for males to intercept females. Experiments in plastic pools compared sites with 20 males: 5 females (simulating hot spots) to pools with 5 males: 5 females. The rate of male harassment of females was higher in 20:5 pools as compared to 5:5 pools. In response to increased male harassment, females reduced their activity on the water and increased their time spent out of the water and thus unable to forage. Males showed a large male mating advantage (LMMA) in 5:5 pools, but, surprisingly, not in 20: 5 pools. This pattern can explain the field observation that small males prefer hot spots. A behavioral mechanism that can explain the LMMA is as follows. Mating occurs when males overcome female resistance. Larger males have a mating advantage over smaller males if females resist heavily. Increased harassment (e.g., in 20:5 pools as compared to 5:5 pools) might result in reduced female resistance to males and thus a reduced LMMA. Females also showed some non-random mating by size that might reflect an interplay between male preference for large females and the avoidance of males by large females. Correspondence to: A. Sih     

Male genital traits and mating interval affect male fertilization success in the water strider Gerris lacustris

Parker's seminal work brought attention to the possibility of postmating sexual selection by non-random fertilization success. Mechanisms for these processes are still only partly understood and there is clearly a need for more studies of intraspecific variation in sperm precedence. Here, we report results from an experimental study of the variation in fertilization success between males of the water strider Gerris lacustris. Genital morphology, male body size, and copulation duration were examined as possible correlates of paternity. The significance of guarding duration was also analysed. Only male genital morphology was correlated to fertilization success. This is one of the first studies showing a relationship between male genital traits and fertilization success, supporting the view that sexual selection may be responsible for the rapid and divergent evolution of genital structures in animals with internal fertilization. The fertilization success of last males varied considerably after double matings with a short mating interval (10 min). Last-male priority ranged from 0 to 100% and usually one of the males involved fertilized almost all the eggs. After double matings with a short mating interval, the proportion of eggs fertilized by the last male averaged 0.68 and was greater than 0.5. In contrast, the average fertilization success was biased towards the first male when the matings were more spread out over time (24 h). These results do not support earlier suggestions of a widespread last-male sperm priority in water striders. Received: 28 July 1998 / Received in revised form: 15 March 1999 / Accepted: 28 March 1999     

Dissecting the tragedy: A spatial model of behavior in the commons

Much of the discussion of the tragedy of the commons focuses on aggregate impacts, often in data-poor developing country settings. Few non-experimental empirical studies shed light on contextual circumstances driving the extent of rent dissipation and overexploitation. We utilize a high-resolution data set to estimate a behavioral model of fishermen's spatial choices. A unique policy setting allows us to measure the degree to which individual fishermen's choices appear aimed at mitigating the tragedy of the commons in a small numbers setting. We find evidence of partial mitigation in excess of what we would expect under pure self-interest but short of what would occur under group-maximizing behavior. We also examine how contextual factors in the fishery shape the degree of cooperation within the fishing season and find evidence that competition for the common pool resource distorts fishermen's implicit cost of distance—creating a form of “common property inertia”.     

The tragedy of the commons in international fisheries: An empirical examination

Historically, all capture fisheries have proven hard to manage; internationally shared stocks face an additional impediment to effective management. Previous fisheries studies estimate gains from cooperation for particular species or locations, but evidence is lacking on the wider effect that international sharing has in relation to other variables that affect stock status. This paper is an attempt to shed a broader light on the effect of sharing by identifying whether shared fish stocks are systematically more exploited. I compile exploitation status, biological and economic data into a unique two-period panel of more than 200 fish stocks from around the globe with which I test the theoretical implications of sharing. The empirical results from ordered category estimation suggest that shared stocks are indeed more prone to overexploitation.     

Male copulatory guarding enhances female foraging in a water strider

Summary In the laboratory, females of Gerris remigis foraging singly after being separated from a copulating male averaged 16 times longer to repel male copulatory attempts compared to repelling time when copulating (60 trials). In<10 min after separation, all females either became immobile at the edge (in 34% of all trials), or recopulated and either continued to forage (61%) or swam to the edge and became immobile (5%). Copulating females captured 85% of imitation prey, but single females, harassed by males, captured only 32% of prey.During a census of 2 small streams, in the pools with swimming single males, >99% of all swimming females were copulating, <1% being single. Ninety seven percent of all single females were immobile at the edge, whereas only 11% of all pairs were at the edge. In pools without swimming single males, 32% of all single females were swimming, compared to <1% in pools with swimming males. Introductions of a male into 4 pools with a female swimming singly in each resulted in the females either becoming immobile at the edge or copulating. The 2 streams had a : sex ratio of 1.6:1, and 79% of all females were copulating during the census. Foraging, copulation and copulatory attempts continued at a reduced level during the night.Thus in streams where male G. remigis are attempting to copulate, females can forage effectively only by carrying a copulating male who apparently repels copulatory attempts by other males.     

Aggressive male mating behavior depends on female maturity in Octopus bimaculoides

This laboratory study examined the combined effects of male and female behaviors on the outcome of mating encounters in Octopus bimaculoides. We found that male–male competition for mating opportunities depends on female maturity; the presence of immature females elicited significantly higher levels of aggression between competing males. We conclude that males are able to assess the reproductive status of females. The study also found that immature and mature females resisted male mating attempts to a similar extent but that males that showed more aggression toward male competitors were able to spend more time in contact with females. We suggest that the lack of prominent visual displays in these mating trials indicates the importance of chemical cues in Octopus mating systems, as has been demonstrated for other cephalopods. This study contributes to the growing research on cephalopod mating systems and in particular shows that Octopus mating dynamics may be more behaviorally complex than initially assumed.     

A free lunch in the commons

We derive conditions under which raising costs through a regulatory constraint or a fully expropriated tax can increase the profits arising from a common-pool resource. The basic model assumes a fixed number of identical agents with linear costs selling in a single period at an exogenous price. A necessary and sufficient condition for a cost increase to be profitable is that aggregate output from the resource be locally convex in aggregate effort. We also show that cost increases can be profitable even if price is endogenous, agents are heterogeneous, entry is costless, or agents are playing a Markov-perfect equilibrium of a dynamic game. We also discuss more general welfare implications of the result along with its relation to existing results for a Cournot oligopoly.     

Analysis of the causal components of assortative mating in water striders

Field studies demonstrate that natural populations of a group of water striders (Heteroptera: Gerridae) that share a common mating system are characterized by weak assortative mating by size and by large sizes of mating males and females relative to single individuals. This study presents an experimental assessment of the components of mating that may contribute to these mating patterns. The effects of male and female body size on each of three components of mating were studied in three water strider species in the laboratory. Large females of all three species mated more frequently, copulated for longer and were guarded longer than small females. Large males mated more frequently than small males in all three species, and also guarded females for longer in the two species where the average of mate guarding was long. However, we found an antagonistic effect of male size on copulation duration: small males copulated for longer than large males in all three species. We show that the combined effects of these size biases mimic the mating patterns found in the wild, e.g. weak and variable assortative mating, and stronger and less variable size ratios of mating versus non-mating females relative to males. We suggest that the antagonistic effects of male size on copulation and guarding duration may be a key source of interpopulational variation in assortative mating and sexual selection on male size. Further, neither spatial or temporal covariation in size, nor mechanical constraints, caused the assortative mating observed here in this group of water striders. Some combination of male and female choice (either active or passive forms) of large mates and male-male exploitation competition for mates play potentially important roles in producing population level assortative mating in water striders. Received: 17 March 1995/Accepted after revision: 28 October 1995     

Foraging in groups of water striders (Gerris remigis): effects of variability in prey arrivals and handling times

Summary In many species, socially subordinate individuals frequently remain in a group despite their lower priority of access to food and mates. This is expected to occur when the net benefits of staying in the group exceed those of a solitary existence. Analogously, territorial foragers surrounded by conspecific competitors are faced with tradeoffs as to patch tenacity. In either case, spatio-temporal variability in resource availability directly affects behavioral patterns and payoffs, particularly of individuals with low priority of access to the resource. However, such individuals may take advantage of natural environmental fluctuations in resource supply in cases where dominants are preoccupied. This arises regularly if two resource items cannot be handled simultaneously and if a second item arrives before handling of the first has been completed. I advance a heuristic model that predicts that foraging or mating success of individuals with low priority of access to resources may increase both with higher variance in inter-arrival times of the resource (given the same mean) and with an increase in the average handling time of the resource. I tested both predictions with two associations of individually marked, naturally foraging water striders (Gerris remigis) in the field. In natural streams individual water striders tend to occupy consistent positions that they may defend, resulting in priority of access to prey items floating downstream for individuals further up front. I manipulated the variance in prey inter-arrival times given the same mean, and the prey handling times by offering larger prey. The outcome was in qualitative agreement with the predictions of the model.     

Fighting behaviour as a correlate of male mating success in black grouse Tetrao tetrix

Fighting is a fundamental determinant of male fitness in species where females prefer socially dominant males as mates or where dominants can prevent subordinates from mating. This in turn can lead to the evolution of honest inter- and intra-sexual cues of male dominance. Fighting as a behaviour comprises both fighting rate (number of fights per unit of time) and fighting performance (success in winning fights), but it is not always clear which of these components are important for female choice and how they link to signals of male quality. To quantify the relative importance of fighting as a cue for females, we recorded detailed behavioural data from male black grouse Tetrao tetrix at leks. We explored the relationship between phenotypic traits (body mass, eye comb size, tail (lyre) length and blue chroma colouration) and fighting performance and rates and how these were related to male mating success. In older males' pairwise fights, winners had lower blue chroma than losers, but there were no differences in other morphological traits. In yearlings, no morphological trait predicted success in pairwise contests. Both fighting rate and performance were positively related to the number of copulations acquired by a male; however, when controlled for lek centrality, fighting performance and not fighting rate was significantly related to mating success. Our results indicate that females may be using components of fighting behaviour as cues for mate choice.     

Male mating effort in a polygynous ungulate

Survival and mating success are key fitness components of mammalian males. Because energy is limited, life history theory predicts trade-offs between current and future reproduction. While many studies have examined fitness trade-off in females, we know little about trade-offs faced by males. In polygynous species, male mating success is largely dependent upon intrasexual competition. Consequently, males have greater uncertainty over the benefits of a given allocation than over its costs, and the correlation between mating effort and success is likely much weaker in males than in females. We analyzed 14 years of data on the mating effort and survival of marked bighorn rams to investigate fitness trade-offs. Dominant rams defended single estrous ewes (“tending”) while subordinates attempted to copulate after separating the tending pair (“coursing”). We estimated the participation in tending and coursing for each ram and the effort in searching for breeding opportunities by each ram each year. We compared these three behavioral indices of male mating effort to demographic parameters, individual characteristics, and both yearly and long-term survival. Mating effort during the rut was unrelated to ram overwinter survival, but longevity was positively correlated with mating effort between 2 and 5 years of age. Persistent variation among rams is likely to explain this pattern, suggesting that in natural populations a few high quality males enjoy both high mating success and high survival.An erratum to this article can be found at     

Strategic mating effort in a simultaneous hermaphrodite

Sexual selection theory for simultaneously hermaphroditic animals predicts an overall preference for inseminating partners that have a relatively higher female fecundity. Previous work on the link between male mating decisions and female fecundity has primarily focused on the effect of the partners’ body size using existing variation in this trait within a study population. On the assumption that the body size is positively correlated with female fecundity, sperm donors should preferentially inseminate relatively larger individuals to obtain a higher fitness gain through their male sex function. However, empirical evidence for such size-dependent mate choice in simultaneous hermaphrodites is equivocal, possibly because of confounding variables. We studied the mating behavior of the simultaneously hermaphroditic flatworm Macrostomum lignano and tested for a strategic mating effort in response to the feeding status of the partner. We experimentally manipulated the feeding status of potential mating partners in order to generate variation in female fecundity among them and tested whether this affected the copulation number and the number of sperm that the focal worm managed to store in the partner’s sperm storage organ. We found that the manipulation of the feeding status had a strong effect on the body size of the potential mating partners and that focal worms copulated more frequently with, and stored more sperm in well-fed partners compared to unfed partners. Our results suggest that M. lignano adjusts its mating effort in response to the feeding status of the mating partner.     

Bateman gradients in a promiscuous mating system

The Bateman gradient is increasingly used to measure sexual selection and characterize mating systems. In a landmark paper, Arnold and Duvall (Am Nat 143:317–348, 1994) formulated predictions about the relationships between sex-specific Bateman gradients and the major types of mating system. In promiscuous species, gradients are expected to be strong and similar in both sexes. Current support for this prediction however remains equivocal as reported male gradients are almost constantly steeper than female gradients. Here, we estimated Bateman gradients in a wild population of Eastern chipmunks (Tamias striatus) over two reproductive seasons characterized by extreme levels of promiscuity and unbiased operational sex ratios. We found significant and positive Bateman gradients for both sexes. The gradients were not different among sexes suggesting that the strength of sexual selection was similar for males and females. The opportunity for selection was also particularly strong for a promiscuous species and not different among sexes. Our results thus support the predicted Bateman gradients for a promiscuous mating system.