Female Pipefish Research Articles

The development of a quantification method for measuring iridescence using sexually selected traits in the Gulf pipefish (Syngnathus scovelli)

Reliably quantifying the strength of visual sexual signals, such as iridescence, has been challenging across the field of evolutionary biology, but is critically important for studying biologically relevant trait variation. To address this issue, we present the Iridescence Detection and Isolation Algorithm (IDIA), which was designed to isolate the iridescent signal from photographs for quantification of ornamentation. The Gulf pipefish, Syngnathus scovelli, served as a model system for testing the limits of the algorithm, and was an ideal test case due to their female-specific iridescent bands on their abdomens with a large degree of among-individual variation. Specifically, we tested the repeatability of iridescence estimates in a variety of settings, including manual versus automated measurements, a gradient of lighting intensities, observational data from multiple populations, and in detecting exposure to synthetic estrogen. Using the IDIA, female iridescence was quantified in two ways with results indicating a manual measurement of each individual band may be more reliable than the automated measurement taken by drawing a polygon around all bands. However, the intensity of the lighting the photographs were taken in did not significantly affect repeatability of the measurement of iridescence no matter how it was taken. The IDIA was able to detect geographical variation in female ornamentation of S. scovelli, demonstrating that our automated approach can potentially replicate previously-described population-level variation. Differences in the iridescent signal were significant when comparing female pipefish from the Florida coast to females collected from the Texas coast, indicating the possibility that external factors, such as differing environmental conditions, could affect the strength of female visual signals. Lastly, the IDIA was applied in an ecotoxicology application to detect the development of iridescence in male pipefish exposed to synthetic estrogen. Exposed males began expressing banding patterns with iridescence levels within the range of females. The results from this study confirm the feasibility of using the IDIA for measuring iridescence in fish across a variety of applications.

Female ornamentation and the fecundity trade-off in a sex-role reversed pipefish.

Sexual ornaments found only in females are a rare occurrence in nature. One explanation for this is that female ornaments are costly to produce and maintain and, therefore, females must trade‐off resources related to reproduction to promote ornament expression. Here, we investigate whether a trade‐off exists between female ornamentation and fecundity in the sex‐role reversed, wide‐bodied pipefish, Stigmatopora nigra. We measured two components of the disk‐shaped, ventral‐striped female ornament, body width, and stripe thickness. After controlling for the influence of body size, we found no evidence of a cost of belly width or stripe thickness on female fecundity. Rather, females that have larger ornaments have higher fecundity and thus accurately advertise their reproductive value to males without incurring a cost to fecundity. We also investigated the relationship between female body size and egg size and found that larger females suffer a slight decrease in egg size and fecundity, although this decrease was independent of female ornamentation. More broadly, considered in light of similar findings in other taxa, lack of an apparent fecundity cost of ornamentation in female pipefish underscores the need to revisit theoretical assumptions concerning the evolution of female ornamentation.

Female pipefish can detect the immune status of their mates

Given the ubiquity of the parasites and their important fitness consequences on mate and offspring condition, selection for the ability to distinguish healthy from parasitized potential mates is a key process to enhance Darwinian fitness. In this study, we experimentally evaluated how the immunological experience of two potential partners influences mate choice, using the sex-role-reversed pipefish Syngnathus typhle. We exposed S. typhle to immune challenges with heat-killed Vibrio bacteria and investigated whether the activation of the immune system determined mate preferences. Our results demonstrate that the immune status of the potential partners influenced female mate preference, such that females that were exposed to an immune challenge became choosy and favored unchallenged males. Males, however, did not show any preferences for female immune status. In this context, we discuss mate choice decisions and behavioral plasticity as a complex result of immune challenge, severity of infection, as well as trans-generational effects.

The Contributions of Premating and Postmating Selection Episodes to Total Selection in Sex-Role-Reversed Gulf Pipefish

Empirical studies of sexual selection often focus on events occurring either before or after mating but rarely both and consequently may fail to discern the relative magnitudes and interactions of premating and postmating episodes of selection. Here, we simultaneously quantify premating and postmating selection in the sex-role-reversed Gulf pipefish by using a microsatellite-based analysis of parentage in experimental populations. Female pipefish exhibited an opportunity for selection (I) of 1.64, which was higher than that of males (0.35). Decompositions of I and the selection differential on body size showed that over 95% of the selection on females arose from the premating phase. We also found evidence for a trade-off between selection phases, where multiply mating females had significantly lower offspring survivorship compared to singly mated females. In males, variance in relative fitness arose mainly from the number of eggs received per copulation and a small number of males who failed to mate. Overall, our study exemplifies a general approach for the decomposition of total selection into premating and postmating phases to understand the interplay among components of natural and sexual selection that conspire to shape sexually selected traits.

Sex-specific responses to fecundity selection in the broad-nosed pipefish

Fecundity selection, acting on traits enhancing reproductive output, is an important determinant of organismal body size. Due to a unique mode of reproduction, mating success and fecundity are positively correlated with body size in both sexes of male-pregnant Syngnathus pipefish. As male pipefish brood eggs on their tail and egg production in females occurs in their ovaries (located in the trunk region), fecundity selection is expected to affect both sexes in this species, and is predicted to act differently on body proportions of males and females during their development. Based on this hypothesis, we investigated sexual size dimorphism in body size allometry and vertebral numbers across populations of the widespread European pipefish Syngnathus typhle. Despite the absence of sex-specific differences in overall and region-specific vertebral counts, male and female pipefish differ significantly in the relative lengths of their trunk and tail regions, consistent with region-specific selection pressures in the two sexes. Male pipefish show significant growth allometry, with disproportionate growth in the brooding tail region relative to the trunk, resulting in increasingly skewed region-specific sexual size dimorphism with increasing body size, a pattern consistent across five study populations. Sex-specific differences in patterns of growth in S. typhle support the hypothesis that fecundity selection can contribute to the evolution of sexual size dimorphism.

An intimidating ornament in a female pipefish

A sexually selected signal may serve a dual function being both attractive to mates and deterring rivals. Presently, there are few unambiguous demonstrations of an ornament functioning in both a mate choice and mate competition context and none regarding female ornaments. We have shown earlier that a temporary ornament, a striped pattern, in a sex-role reversed female pipefish, Syngnathus typhle, attracts males. Here we show that this ornament also intimidates rival females: in one experiment a male could interact with either 1 or 2 females. Latency until copulation was longer when 2, rather than 1, females were present. Moreover, when 2 females were present, competition lasted longer and time until mating took place increased when females displayed their ornaments more equally. In another experiment, a focal female could see 1 stimulus female and 1 stimulus male, the latter 2 being unaware of each other. The ornament of the stimulus female was manipulated, either strengthened by being painted black or left unaltered by being sham-painted. As a result, focal females experiencing black-painted stimulus females decreased courtship as well as competitive activities compared with focal females seeing sham-painted females. Moreover, focal females seeing black-painted females displayed less of their own ornament compared with controls. This decrease was due to a decrease in display toward males rather than to stimulus females. Thus, this female ornament indeed has a dual function, attracting mates and deterring rivals. In addition, the social costs invoked by this intimidating effect on rivals may help to maintain signal honesty.

Male but not female pipefish copy mate choice

If mate choice is costly, an individual may reduce the costs of choice by observing and copying the mate choice of others. Although copying has received much attention during the past 10 years, evidence of copying is not very strong, partly because of problems with distinguishing copying from other mechanisms creating similar mating patterns. I conducted an aquarium experiment using the deep-snouted pipefish Syngnathus typhle, a species with reversed sex roles and mutual mate choice. I tested whether copying occurred both during male and female mate choice. The results showed that males, but not females, displayed more toward an individual, which they perceived as popular among others, and this was interpreted as male mate choice copying. While being the first evidence of copying in a sex-role--reversed species, the sex difference in behavior mirrors the sex-role pattern and begs the question whether we should predict copying only in females in other species with mutual choice but conventional sex roles. Copyright 2006.

Sex-role reversal revisited: choosy females and ornamented, competitive males in a pipefish

In the pipefish Syngnathus typhle sex roles are reversed, that is, females compete more intensely than males over mates. However, competition over mates among individuals of one sex does not necessarily prevent members of that same sex from being choosy, and choosiness in the other sex does not prevent competition within it. In an experiment we allowed a female pipefish to choose freely between two males, after which we released the males and let the three interact. Comparisons with earlier results show that both sexes courted partners and competed with consexuals. However, females courted more often than did males, and courtship was more frequent in treatments involving large individuals than in treatments with small individuals. Males competed among themselves for access to mates but for a shorter duration than females in the same situation. Males displayed an ornament towards females but not to males during mating competition. Females, however, used their ornament in both contexts. Females did not always mate with the male of their previously made choice, which we interpret as females being constrained by male-male competition, male motivation to mate, or both. Thus, in this sex-role reversed species, mate choice in the more competitive sex may be circumvented and even overruled by mate competition and mating willingness in the least competitive sex. Hence, sex roles should not be considered as sexes being either choosy or competitive but rather that males and females may exhibit different combinations of choice and competition.

Reproductive Ecology and Operational Sex Ratio of Worm Pipefish(<i>Nerophis lumbriciformis</i>) in Irish Waters

Worm pipefish (Osteichthyes, Syngnathidae) are common members of the ichthyofaunal commu nity on rocky shores in western Europe. However, there has been little research into their biology and ecology. Male Nerophis lumbriciormis, like all syngnathids, brood eggs to hatching on a modified area on their abdomen. Worm pipefish are engaged in reproductive activity from January to October. During this period approximately two-thirds of the mature fish are capable of reproduction. Egg-beanrng males carry a mean of 49.5 eggs (SE + 1.4) in each brood. Male reproductive potential is dependent on the resources available to female pipefish for the generation of oocytes (clutch). While there was no significant difference in the median numbers in broods or clutches, the number of oocytes in female ovaries (55.17+ 1.77 (SE)) exceeds mean brood size. It is hypothesised that female pipefish are capable of mating with more than one male. The operational sex ratio (ratio of available males to females) from April to June is heavily biased towards female pipefish. Therefore, male pipefish become a reproductively-limiting resource for females during these months.

Reproductive Ecology and Operational Sex Ratio of Worm Pipefish (Nerophis lumbriciformis) in Irish Waters

Worm pipefish (Osteichthyes, Syngnathidae) are common members of the ichthyofaunal community on rocky shores in western Europe. However, there has been little research into their biology and ecology. Male Nerophis lumbriciformis, like all syngnathids, brood eggs to hatching on a modified area on their abdomen. Worm pipefish are engaged in reproductive activity from January to October. During this period approximately two-thirds of the mature fish are capable of reproduction. Egg-bearing males carry a mean of 49.5 eggs (SE ± 1.4) in each brood. Male reproductive potential is dependent on the resources available to female pipefish for the generation of oocytes (clutch). While there was no significant difference in the median numbers in broods or clutches, the number of oocytes in female ovaries (55.17 ± 1.77 (SE)) exceeds mean brood size. It is hypothesised that female pipefish are capable of mating with more than one male. The operational sex ratio (ratio of available males to females) from April to June is heavily biased towards female pipefish. Therefore, male pipefish become a reproductively-limiting resource for females during these months.

Inter- and intra-gender analyses of feeding ecology of the worm pipefish (Nerophis lumbriciformis)

Small vagile epiphytic crustaceans formed the greatest proportion of the diet of worm pipefish. There were significant differences in the number (Mann–Whitney U=22006·5, P<0·001) and diversity (Mann–Whitney U=11546·0, P<0·05) of prey consumed by male and female pipefish. Harpacticoid copepods are the most numerically dominant form of prey consumed. Further gender analysis of mature pipefish revealed that reproductively mature females and egg-bearing male worm pipefish show significantly greater predatory effort (Kruskal–Wallis H=24·15, df=2, P<0·001). Increased feeding activity, within these groups, is suggested to alleviate the substantial reproductive costs for both female and egg-bearing male pipefish.

Balancing sexual selection through opposing mate choice and male competition

Male–male competition and female mate choice act contemporaneously in the cockroach Nauphoeta cinerea and the social pheromone of males influences the outcome of both forms of sexual selection. We therefore examined the joint and separate effects of male–male competition and female mate choice to determine if the selective optima for the pheromone were the same or different. Dominant males in a newly established hierarchy mated more frequently, but not exclusively. Manipulations of the multi-component social pheromone produced by males of N. cinerea showed that both long- and close-range attraction of females by males were influenced by the quantity and composition of the pheromone. The most attractive composition, however, differed from that which was most likely to confer high status to males. Since the outcome of male–male competition can conflict with mating preferences exhibited by females, there is balancing sexual selection on the social pheromone of N. cinerea. Such balancing selection might act to maintain genetic variation in sexually selected traits. We suggest that the different forms of sexual selection conflict in N. cinerea because females prefer a blend different to that which is most effective in male–male competition in order to avoid mating with overly aggressive males.

Female sand gobies prefer good fathers over dominant males

Female preference for males successful in male–male competition is generally assumed to result in mating with high quality males. Here I report results from an experiment disentangling the effects of intra– and intersexual selection in the sand goby, Pomatoschistus minutus , a marine fish that exhibits paternal care. I show that large males are successful in male–male competition, but contrary to what one would expect, dominants are not preferred by females and are not better at taking care of the eggs. Female preference, however, correlated with the subsequent hatching success of the eggs. Thus, female choice selects for good parenting. Hence, direct benefits in the form of superior paternal care can explain female choice in this species, supporting a good parent process of sexual selection. However, choosing on the outcome of male–male competition does not enable females to mate with the ‘best’ males.

Ornamentation predicts reproductive success in female pipefish

In the sex-role reversed pipefish Syngnathus typhle females compete for access to males and males are choosy. Females develop a temporary ornament when competing over mates with other females and when performing nuptial dances with males. This ornament is an amplification of the normal striped pattern in these fishes. We here show experimentally that (1) the contrast of this normal pattern forecasts the extent to which the ornament is shown, (2) contrast and ornamentation honestly signal female quality (egg numbers), (3) contrast and ornamentation accurately predict female mating success, (4) contrast is a phenotypically plastic trait specifically exaggerated under situations of female – female competition, and (5) neither contrast nor ornament are energetically expensive to the females (i.e., they are independent of short-term nutritional status). Hence, as predicted in sex-role reversed species, ornament design is constrained by costs to female fecundity: an energetically demanding ornament would impair on a female's ability to produce eggs. The type of ornament described here is the expected one, costly for reasons other than being energetically expensive to produce.