Sex-biased movement in the guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>)

The movement strategies of birds and mammals are often closely linked to their mating system, but few studies have examined the relationship between mating systems and movement in fishes. We examined the movement patterns of the guppy (Poecilia reticulata) in the Arima river of Trinidad and predicted that sexual asymmetry in reproductive investment would result in male-biased movement. Since male guppies maximize their reproductive success by mating with as many different females as possible, there should be strong selection for males to move in search of mates. In agreement with our prediction, the percentage of fish that emigrated from release pools was higher for males than females (27.3% vs. 6.9%, respectively). Sex ratio was highly variable among pools and may influence a male's decision to emigrate or continue moving. We also detected a positive relationship between body length and the probability of emigration for males and a significant bias for upstream movement by males. Among the few females that did emigrate, a positive correlation was observed between body length and distance moved. Sex-biased movement appears to be related to mating systems in fishes, but the evidence is very limited. Given the implications for ecology, evolution, and conservation, future studies should explicitly address the influence of sex and mating systems on movement patterns.     

Mate choice in female convict cichlids (<Emphasis Type="Italic">Amatitlania nigrofasciata</Emphasis>) and the relationship between male size and dominance

We examined how male size and fighting ability influence a female’s mate assessment process and her eventual mate choice in the monogamous convict cichlid, Amatitlania nigrofasciata. Females always chose the larger of two males when they were allowed to see a larger male next to a smaller one and when a larger male defeated a smaller one in a fight. They did not differentiate between large and small males when they did not see the two males together nor did they choose a dominant over a subordinate male when both were the same size. We suggest that females select on the basis of male size because it is a better predictor of both direct and indirect benefits (i.e., future competitive interactions and foraging ability) than dominance behavior only. Despite selecting one male over the other early in the courtship period, females continued to visit both males until spawning. Our evidence suggests that this assessment behavior more closely resembles a bet-hedging tactic rather than the female’s indecision as to which male will be her mate.     

Sexual selection and conflict in the bulb mite, <Emphasis Type="Italic">Rhizoglyphus robini</Emphasis> (Astigmata: Acaridae)

Whether benefits of mate choice accrued by females outweigh costs associated with sexual selection remains largely unresolved. The ‘good genes’ perspective, posing that mate choice benefits females genetically has been challenged by the arguments that sexual selection is driven mostly by direct costs and inter-sexual conflict. Here, I present an overview of experimental tests of predictions of good genes and sexual conflict mechanisms in the bulb mite Rhizoglyphus robini.     

Female fecundity and early offspring growth in the guppy, <Emphasis Type="Italic">Poecilia reticulata</Emphasis>

We examined the relationships between family (female parentage), body size of females, brood retention time between mating and parturition, female fecundity, and early growth of offspring in the guppy Poecilia reticulata. Mature, virgin females from a single brood were mated with a single male. Results of generalized linear models indicate that the effect of the family on female fecundity and offspring growth was significant, which suggested that these traits are genetically determined to a certain extent. Larger females at the time of mating produced larger broods, although female body size at the time of parturition did not affect brood size, in contrast to the results of some previous studies in guppies. Brood size was negatively associated with the body size of neonates. Results highlighted significant associations between brood retention time and female fecundity as well as offspring growth. In addition, the interaction between the family and brood retention time was significantly associated with female fecundity and offspring growth. Females of some families had longer retention times of larger broods, whereas those of other families had shorter retention times of smaller broods. On the other hand, females with longer brood retention times produced smaller neonates with slower growth. Since the family also affected the brood retention time, selection may work against the duration of brood retention of females via the size, growth and number of offspring, depending on environmental factors such as the intensity of predation or competition in neonates.     

Predator-induced plasticity in guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>) life history traits

A number of invertebrates show predator-induced plasticity in life-history and morphological traits that are considered adaptive. Evidence is accumulating that vertebrates may also adjust their life-history traits in response to predators; however, some of the patterns of plasticity, which appear to be an adaptive response specifically to the risk of size-selective predation, may instead result from reduced foraging in response to predator presence. Here, we describe a study of predator-induced plasticity in guppies (Poecilia reticulata). We have predicted that the plastic response to cues from a small, gape-limited, natural predator of guppies, the killlifish (Rivulus hartii), would be the opposite of that caused by reduced food intake. We have found that male guppies increased their size at maturity, both length and mass, in response to the non-lethal presence of this predator. This pattern of plasticity is the opposite of that observed in response to reduced food intake, where male guppies reduce size at maturity. The increase in size at maturity that we observed would likely reduce predation on adult male guppies by this native predator because it is gape-limited and can only eat juvenile and small adult guppies. This size advantage would be important especially because male guppies grow very little after maturity. Therefore, the pattern of plasticity that we observed is likely adaptive. In contrast, female guppies showed no significant response in size at first parturition to the experimental manipulation; however, we did find evidence suggesting that females may produce more, smaller offspring in response to cues from this predator.     

Sperm transfer and paternity in the scorpionfly <Emphasis Type="Italic">Panorpa cognata</Emphasis>: large variance in traits favoured by post-copulatory episodes of sexual selection

Post-copulatory episodes of sexual selection can be a powerful selective force influencing the reproductive success of males. In order to understand variation in male fertilisation success, we first need to consider the pattern of sperm utilisation by females following matings with more than one male. Second, we need to study those traits responsible for male success in sperm competition. Here we study both male sperm transfer characteristics as well as offspring paternity of females mated to two males in the scorpionfly Panorpa cognata. By repeatedly mating males to virgin females and interrupting copulation at defined time points, we found for all males that sperm transfer set off after approximately 40 min. During the remaining copulation, sperm transfer of individual males was continuous and with constant rate. Yet the rate of sperm transfer differed between individual males from about one sperm per minute to more than eight sperm per minute for the most successful males. In addition, we measured the fertilisation success in sperm competition of males with known sperm transfer capability. The relative number of sperm transferred by males during copulation, estimated from copulation duration and the males’ individual sperm transfer rate, explained a large proportion of variation in offspring paternity. The mode of sperm competition in this species, thus, conforms largely to a fair raffle following complete mixing of sperm prior to fertilisation. Hence, male differences in both the ability to copulate for long and of rapid sperm transfer will translate directly into differences in reproductive success.     

Mating success of male guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis> in the wild

To understand how the diversity among male sexual traits is maintained despite directional female choice for attractive traits, it is important to study male reproductive success in each reproductive episode. Male reproductive success is indeed the comprehensive result of several processes such as mate choice, mating, and fertilization. In this study, male mating success was estimated in a wild guppy Poecilia reticulata population of Hiji River, Okinawa Island, in southern Japan. The mating success of males was estimated as the percentage of sperm transferred in relation to the total sperm reserve. In a preliminary experiment, it was confirmed that the sperm reserves of males were partly replenished after 12 h and fully replenished after 72 h, when all sperm were released. In addition, the results of investigation in the wild population revealed that approximately 20% of males had no sperm reserves at all, although their sperm reserves should have been replenished by sexual isolation. Male sexual traits such as body size or color pattern did not affect the percentage of sperm transferred. Results from this study provide important insights into male sperm transfer ability and sperm production in this population. However, the high frequency of male sperm-transfer success estimated in this study should to be taken with caution, and whether it is due to differences between wild and laboratory conditions, sex ratio or the rates of multiple matings by females in the wild population remain to be fully explored.     

Female mate preference based on male orange spot patterns in the feral guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis> in Japan

It is known that females prefer males with larger and/or brighter orange spots in many populations of the guppy Poecilia reticulata. However, female preference for male orange spots varies among populations and changes within several years when they are introduced into new habitats with different environment. Guppies were introduced into Okinawa, Japan, more than 20 years ago and were subjected to natural and sexual selection for a long period. The female preference for orange spot patterns of males was examined by the dichotomous choice experiment for a feral guppy population of the Hiji River, Okinawa. We chose full-sibling males as a pair of stimulus males that were simultaneously presented to a test female, because sibling males should resemble each other. To create different orange spot patterns between stimulus males, one male of the stimulus male pair was fed carotenoid-supplement food such as algae and another male was fed low-carotenoid food. High-carotenoid-treatment males showed not only brighter coloration of orange spots but also larger spots than other males as a result of this dietary-manipulation. In the dichotomous choice experiment, females preferred the high-carotenoid-treatment males. In addition, logistic regression analysis clarified that brighter coloration of male orange spots was the most important factor for female mate preference. This finding suggests indirect benefits of female preference for male orange spot patterns if the male foraging ability for algae were heritable.     

Sperm precedence in <Emphasis Type="Italic">Callosobruchus chinensis</Emphasis> estimated using the sterile male technique

P₂, the proportion of offspring sired by the second male to mate, is an indicator of the outcome of postcopulatory sexual selection, which occurs through sperm competition and/or cryptic female choice. We determined the appropriate dose of gamma radiation for sterilization of adult males and, using the sterile male technique, measured P₂ in the adzuki bean beetle, Callosobruchus chinensis. Adult males of C. chinensis were almost completely sterilized when irradiated at 80 Gy. Thus, we obtained sterile males through irradiation at this dose. Neither the probability of female first mating nor the probability of female remating was affected by whether females were paired with normal or sterile males. The P₂ calculated from the hatching success of eggs laid by females that mated both with normal and sterile males did not differ between reciprocal mating sequences, indicating that the sterilization has no effect on sperm fertilizing ability. The P₂ was estimated at 0.25. This study shows that female remating in C. chinensis means the coexistence of sperm from two males and thus the occurrence of postcopulatory sexual selection within the female reproductive tract, resulting in first-male sperm precedence.     

A Comparison of Female Mating Strategies in <Emphasis Type="Italic">Pan troglodytes</Emphasis> and <Emphasis Type="Italic">Pongo</Emphasis> spp.

Orangutans and chimpanzees differ in many aspects of their mating and social systems. Nevertheless, because both great apes require enormous maternal investment in offspring and because female reproductive potential is limited, female orangutans and chimpanzees should be selective of their mates, yet expected to exhibit anti-infanticide strategies such as mating with multiple males. We review and compare mating patterns in orangutans and chimpanzees to understand how these critical pressures are filtered through the different demands of the socioecology of each species. We highlight the variation in female mating behavior as a function of the proximity of ovulation. We conclude that both genera pursue tactics for paternity confusion by mating with multiple males and by mating cooperatively or even proceptively with nonpreferred partners when conception is unlikely. Mating selectivity is suggested by variation in proceptive behavior toward particular partners and by increased resistance of nonpreferred partners during the periovulatory period. Thus, data for both species support a mixed mating strategy whereby females shift their mating behavior in accordance with ovulatory status to accommodate the competing demands of mate selectivity and paternity confusion.     

Mate choice and sexual conflict in <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> (Rotifera)

Male mate choice in Brachionus plicatilis is based on information from coronal receptors and contact chemoreception of a glycoprotein signal on the body surface of females. Male mating behavior is modulated by mating signal quality and strength, which determines male mating persistence and circling intensity. We probe the sensory abilities of males by better resolving their discrimination of female age. Males preferentially initiate mating with young females, but not too young. Males circle 0.2 h old females just hatched from resting eggs only about 1/2 as frequently as 12 h old females. Males are even more discriminating of females with whom they copulate, preferring 3 h old females significantly more than 0.2 h or 6 h old females. In contrast, males cannot distinguish between virgin females and those who have already copulated. Similarly, males circled and copulated with females hatching from resting eggs with equal frequency as those hatching from amictic eggs. The counterpoint to male mate choice is female resistance to mating. When males contact females, the females respond with one of four behaviors: no response, acceleration, foot flipping, or coronal retraction. In 65% of male–female encounters, there was no initial response by females. However, when males began circling females, females accelerated 11.1 times more often than when males were absent. The second type of evasive female behavior was foot-flipping, which tends to knock off males attempting to circle the female. In the presence of circling males, females performed foot-flipping behavior three times more often than in the absence of males. Coronal retraction, where they stop swimming and withdraw their corona, was observed less frequently than acceleration or foot-flipping, and there was no difference in the presence or absence of males. These data are interpreted in the context of sexual conflict, where the behaviors that optimize male and female fitness differ. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Inbreeding influences herbivory in <Emphasis Type="Italic">Cucurbita pepo</Emphasis> ssp. <Emphasis Type="Italic">texana</Emphasis> (Cucurbitaceae)

In a series of field experiments Diabrotica beetle herbivory was found to influence the magnitude of inbreeding depression in Cucurbita pepo ssp. texana, an annual monoecious vine. Beetles damage flowers and fruits and chew dime-sized holes in leaf tissue between major veins. Inbred plants were found to be more likely to be damaged by beetles and to have more leaves damaged per plant than outcrossed plants. A positive linear association was found between the coefficient of inbreeding and the magnitude of leaf damage, whereas a negative association was found between coefficient of inbreeding and several male and female fitness traits. When pesticides were used to control beetle herbivory, the interaction between coefficient of inbreeding and pesticide treatment was significant for fruit production and marginally significant for pollen quantity per anther. Therefore, the magnitude of inbreeding depression in C. pepo ssp . texana varies depending on the severity of beetle herbivory.     

Nonvisual mate choice in the Pyrenean mountain newt (<Emphasis Type="Italic">Euproctus asper</Emphasis>): females prefer small males

In many species, females prefer large males as mates. In this paper, we examined whether female Pyrenean mountain newts (Euproctus asper) would show a preference for large males in a simultaneous choice situation. When we tested for a visual preference relative to male body size using visual cues, females did not prefer large males. When chemical cues were presented, females did show a preference, but contrary to our prediction, they preferred the smaller of two males. E. asper males exhibit coercive mating behavior (amplexus), keeping females from feeding for several hours or even days, which may explain why females avoid large, physically stronger, and thus, more coercive males. The predominantly nocturnal lifestyle may explain why visual cues are less important for mate discrimination in this species.     

Long-wavelength sensitive visual pigments of the guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>): six opsins expressed in a single individual

Background

The diversity of visual systems in fish has long been of interest for evolutionary biologists and neurophysiologists, and has recently begun to attract the attention of molecular evolutionary geneticists. Several recent studies on the copy number and genomic organization of visual pigment proteins, the opsins, have revealed an increased opsin diversity in fish relative to most vertebrates, brought about through recent instances of opsin duplication and divergence. However, for the subfamily of opsin genes that mediate vision at the long-wavelength end of the spectrum, the LWS opsins, it appears that most fishes possess only one or two loci, a value comparable to most other vertebrates. Here, we characterize the LWS opsins from cDNA of an individual guppy, Poecilia reticulata, a fish that is known exhibit variation in its long-wavelength sensitive visual system, mate preferences and colour patterns.

Results

We identified six LWS opsins expressed within a single individual. Phylogenetic analysis revealed that these opsins descend from duplication events both pre-dating and following the divergence of the guppy lineage from that of the bluefin killifish, Lucania goodei, the closest species for which comparable data exists. Numerous amino acid substitutions exist among these different LWS opsins, many at sites known to be important for visual pigment function, including spectral sensitivity and G-protein activation. Likelihood analyses using codon-based models of evolution reveal significant changes in selective constraint along two of the guppy LWS opsin lineages.

Conclusion

The guppy displays an unusually high number of LWS opsins compared to other fish, and to vertebrates in general. Observing both substitutions at functionally important sites and the persistence of lineages across species boundaries suggests that these opsins might have functionally different roles, especially with regard to G-protein activation. The reasons why are currently unknown, but may relate to aspects of the guppy's behavioural ecology, in which both male colour patterns and the female mate preferences for these colour patterns experience strong, highly variable selection pressures.

     

Plasticity in courtship and sneaking behaviors depending on tail length in the male guppy, <Emphasis Type="Italic">Poecilia reticulata</Emphasis>

Male guppies Poecilia reticulata exhibit two types of mating behavior, i.e., courtship displays for cooperative copulation and sneaking attempts for forced copulation. The frequencies of the two male mating behaviors are influenced by tail length. Males possessing long tails exhibit courtship displays less frequently and sneaking attempts more frequently than those possessing short tails, even though they have similar total lengths. To examine whether these male behavioral tendencies depending on tail length are genetically controlled or are determined by tail length per se, tail length manipulation was conducted. The tail lengths of males that had previously possessed longer tails were surgically shortened to a greater degree than those of their counterparts that had previously possessed shorter tails. Although the frequencies of the mating behaviors exhibited by the latter males did not apparently change, the former males clearly increased the frequency of courtship displays and decreased that of sneaking attempts following tail shortening. These results indicate that males adjust the frequencies of the two mating behaviors according to their tail length. Since females avoid cooperative mating with males possessing long tails, the change in mating behavioral patterns by males depending on their tail length may increase their mating opportunities.     

Cave molly females (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>) avoid parasitised males

Cave mollies (Poecilia mexicana) inhabit a dark Mexican cave, where visual communication is impossible. I observed the preference of cave molly females to associate with a non-infected male or a male infected with a pathogenic bacterium (Mycobacterium sp.) which causes the formation of large blisters around the eyes of infected fish. Females preferred to stay near the non-infected male only when the two stimulus males were separated from the female by transparent Plexiglas in light, but not when the males were separated by a wire-mesh in light (where vision was to some extent hindered, but the females perceived non-visual cues) or in darkness (where only non-visual cues were available). I conclude that the visually mediated preference for non-infected males has been maintained during the colonisation of the lightless habitat, but a preference for this trait on the basis of non-visual cues did not evolve. The cave habitat may be poor in pathogens, resulting in low selection pressure to evolve a non-visual preference for males without bacterial infection.Communicated by R.F. Oliveira     

Polymorphic microsatellite loci in the Australian tree frog, <Emphasis Type="Italic">Litoria peronii</Emphasis>

Eleven novel polymorphic microsatellite loci developed from a microsatellite enriched genomic library, are presented for the Australian tree frog Litoria peronii. We screened 29 individuals from a single population and detected high levels of polymorphism for all 11 loci with the number of alleles/locus ranging from 9 to 24. Values of expected and observed heterozygosities ranged from 0.789–0.955 and 0.207–1.00, respectively. These microsatellite markers should prove useful in determining levels of genetic diversity, measuring gene flow and migration, assigning individuals to their most likely population of origin, and in the assignment of paternity.     

Sociality in <Emphasis Type="Italic">Euglossa</Emphasis> (<Emphasis Type="Italic">Euglossa</Emphasis>) <Emphasis Type="Italic">viridissima</Emphasis> Friese (Hymenoptera,Apidae, Euglossini)

Euglossa viridissima is an orchid bee that forms both solitary and multiple female nests, making it a suitable species for the study of factors leading to diverse degrees of sociality in Euglossines. We conducted observations in eight reused nests (where a first generation of bees had been produced) kept in artificial boxes from the Yucatan Peninsula, Mexico. Five nests were reused (reactivated) by a single female (SFN), two nests reused by a mother and one daughter (MFN1) and one nest reused by the mother and two daughters (MFN2). No single nest was reactivated by unrelated females. The number of foraging trips, their duration and the duration of cell provisioning was not different between SFN and MFN. The overall production of cells per female was not different either between both types of nest. However, in MFN although all females did lay eggs, there was a reproductive skew in favor of the mother (95 and 45% of the brood produced in MFN1 and MFN2 respectively). She showed reproductive control of her daughters through oophagy and displaying threatening behavior when the daughters tried to open a cell where she had laid an egg. Brood losses to parasites (Anthrax sp. (Bom-byliidae) and Hoplostelis bivittata (Megachilidae)) were only found in SFN which possibly reflects and advantage of MFN in this respect. Our results coupled with other studies in Euglossa, reveal that a wide range of social behaviors occur in this genus, from solitary and communal to primitive reproductive division of labor. Multiple factors involving different levels of pressure imposed by food availability and parasites may favor such a diverse range of nesting behaviors. Interestingly, female associations in E. viridissima seem a result of kin selection that is enforced by coercion from mother females on their daughters. More studies are needed to shed light upon the social organization of Euglossa and other Euglossines and on their phylogenetic relationships in order to trace the origins of eusociality in Apidae. Received 12 February 2008; revised 25 June 2008; accepted 17 July 2008.     

<Emphasis Type="Italic">Sporidiobolus johnsonii</Emphasis> and <Emphasis Type="Italic">Sporidiobolus salmonicolor</Emphasis> revisited

The relationship between Sporidiobolus johnsonii and S. salmonicolor was investigated using rDNA sequence data. Two statistically well-supported clades were obtained. One clade included the type strain of S. johnsonii and the other included the type strain of S. salmonicolor. However, some mating strains of S. salmonicolor were found in the S. johnsonii group. These strains belonged to mating type A2 and were sexually compatible with mating type A1 strains from the S. salmonicolor group. DNA–DNA reassociation values were high within each clade and moderate between the two clades. In the re-investigation of teliospore germination, we observed that the basidia of S. salmonicolor were two-celled. In S. johnsonii, basidia were not formed and teliospore germination resulted in direct formation of yeast cells. We hypothesize that the S. johnsonii clade is becoming genetically isolated from the S. salmonicolor group and that a speciation process is presently going on. We suspect that the observed sexual compatibility between strains of the S. johnsonii and S. salmonicolor groups and the possible genetic flow between the two species has little biological relevance because distinct phenotypes have been fixed in the two taxa and intermediate (hybrid) sequences for LSU and ITS rDNAs have not been detected. An erratum to this article can be found at