Why clean and be cleaned? The importance of client ectoparasites and mucus in a marine cleaning symbiosis

The preferences exhibited by cleaner fishes for particular client species and the high variability in rates at which various clients visit cleaning stations have remained largely unexplained. In this study, we assessed the relative importance of client ectoparasite load and mucus characteristics for the behaviour of cleaning gobies, Elacatinus spp, and their fish clients on a Barbadian fringing reef. Client species with high ectoparasite loads visited cleaning stations more often than less parasitised species. This effect was independent of body size. Frequency of visits to cleaning stations was not related to client mucus characteristics. These results suggest that the main motivation for clients to interact with cleaners is ectoparasite removal. Cleaners did not preferentially clean clients with higher ectoparasite load or better mucus, nor did they spend more time inspecting such clients. The interests of cleaners and clients therefore appear to be inconsistent. This may be due to the generally low rate of ectoparasitism on Barbadian fish compared to fish of other regions. Cleaning gobies fed at a lower rate on client species with higher loads of gnathiid isopod larvae, which may be explained if cleaners switch from eating ectoparasites to other items, such as mucus, on clients with few ectoparasites. Our estimates of caloric and protein content of fish mucus suggest that it may be as valuable a food source per unit weight as ectoparasites. However, no data are available to compare the value of each item per unit feeding time. The fact that clients with few ectoparasites still visit cleaners, albeit at a low rate, suggests that the cost of mucus removal may be low, compared to the benefit of incidental parasite removal. Thus, the outcome of cleaning interactions may remain positive, even in areas characterised by naturally low parasitism on clients.     

Sociality, exotic ectoparasites, and fitness in the plural breeding rodent Octodon degus

Social animals are susceptible to high infection levels by contact-transmitted parasites due to increased conspecific interaction. Exotic parasites are known to have adverse consequences on native hosts. We examined the relationship between social group size and exotic ectoparasite loads, and adult infection levels with per capita fitness and offspring survival in the plural breeding rodent Octodon degus in central Chile. Degus at our site were almost entirely infected by two exotic ectoparasites: the fleas Leptopsylla segnis and Xenopsylla cheopis. Neither group size nor number of females per group predicted the abundance of either exotic flea species. The per capita number of pups (per capita fitness) that emerged from burrow systems used by known social groups was negatively correlated with abundance of L. segnis but not X. cheopis. On adults, X. cheopis abundance was three times greater than L. segnis but was not significantly correlated with per capita fitness. In females, L. segnis abundance was negatively correlated with peak body mass during pregnancy. Adult ectoparasite load was not correlated with offspring survival. Based on these results, we hypothesize that high infection levels of L. segnis result in decreased reproductive fitness of adult female degus but are not a cost of sociality because parasite loads are not predicted by social group size. Further work is needed to experimentally test this hypothesis and to determine if L. segnis serves as a vector for a deleterious pathogen. Lastly, the lack of native ectoparasites may explain why a previous study at our site determined that behavioral adaptations needed to cope with high ectoparasite burdens (e.g., grooming) are not extensive in degus; they simply have not had the coevolutionary time needed for selection of these behaviors.     

Ectoparasites of house sparrows (Passer domesticus): an experimental test of the immunocompetence handicap hypothesis and a new model

Conspicuous secondary sexual traits may have evolved as handicap-revealing signals or as badges of status. We present results of an experiment using males of the sexually dimorphic house sparrow (Passer domesticus), that support the idea that the male-specific bib can be both a handicap-revealing signal and a reliable badge indicating the physical condition of the bird. In a test of the immunocompetence handicap hypothesis, wild-caught adult male house sparrows were studied in captivity. Birds implanted with elevated doses of testosterone were more dominant, had higher circulating levels of both testosterone and corticosterone and they also harboured relatively larger ectoparasite loads. Higher parasite loads were also associated with individuals showing lower immunocompetence and larger changes in bib size. A new model for immunocompetence effects in sexual selection is introduced, integrating actions that the hypothalamopituitary axis exerts on gonads, adrenals and the thyroid gland. The ”integrated immunocompetence model” synthesizes both the ”handicap” (i.e. survival-decreasing) and ”badge of status” (i.e. survival- enhancing) models for evolution of secondary sexual traits. Received: 15 May 1999 / Received in revised form: 2 November 1999 / Accepted: 6 November 1999     

Female choice for parasite-free male satin bowerbirds and the evolution of bright male plumage

Summary Hamilton and Zuk proposed that bright male plumage may have evolved in males of polygynous species as a result of female preferences for males that are able to demonstrate their resistance to disease. They predicted an inverse correlation between female mating preferences and the level of parasitic infection of males. We found such a correlation between the level of infection by a common ectoparasite (Myrsidea ptilonorhynchi: Menoponidae) and mating success of male satin bowerbirds (Ptilonorhynchus violaceus). In addition, we tested and were able to confirm three other predictions derived from their model: that (1) older males had fewer parasites than their younger counterparts, (2) levels of individual parasitic infection are highly correlated between years, and (3) that individuals resighted in successive years are less parasitized than those that fail to return. These results support the bright male model, but they are also consistent with two other hypotheses that may explain plumage dimorphism based on the level of parasitic infection. The correlated infection model suggests that females choose males with few ectoparasites because of a correlation between the level of ectoparasitic infection and heritable resistance to internal infections. In the parasite avoidance model, females favor parasitefree males because it lowers their own prospects for parasitic infection. Our data did not show the predicted relationship between parasite numbers with plumage quality that is needed to support the bright male hypothesis, nor did it show the inverse correlation between male condition and parasite numbers that is predicted by both the bright male and correlated infection hypotheses. Our results are most consistent with the parasite avoidance hypothesis.     

The effects of two acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on pairing success in male Gammarus pulex (Crustacea: Amphipoda)

Parasites can decrease male mating success in host species in various ways, in particular by affecting male competitive ability for access to females. However, male-male competition can take different forms (i.e. interference vs exploitation competition) and which type of competition is most affected by parasites is not always clear. We investigated the influence of two acanthocephalan parasites Pomphorhynchus laevis and Polymorphus minutus on the pairing success of their intermediate host, Gammarus pulex, using field-based studies and complementary laboratory-based studies. We first studied male pairing success in the field using four large samples of paired and unpaired individuals collected at different dates. In three of the samples, the effects of size and parasite infection were significant, whereas for one sample only male size had a significant effect. There was no difference in size distributions between infected and uninfected gammarids. Large males were paired more often than smaller males, and uninfected males were paired more frequently than infected males, the pairing success of P. minutus-infected males being more severely affected than that of P. laevis-infected males. We then experimentally tested the ability to enter into precopula with a receptive female in the presence or absence of competitors. In competitive situations, the pairing success of P. laevis- and P. minutus-infected males was significantly lower than that of uninfected males, with pairing success being more affected in P. laevis-infected than in P. minutus-infected males. In the absence of competition, males infected with P. laevis were significantly less likely to enter into precopula compared with uninfected males and P. minutus-infected males, whereas there was no difference between uninfected and P. minutus-infected males in their inclination to pair with a receptive female. However, for both parasites, latency time to pair formation was significantly shorter for uninfected than for infected males. In a third experiment, we tested for a potential effect of vertical segregation on the pairing success of infected and uninfected males, but found no evidence for it. We conclude that infected males may be less competitive than uninfected males in competition by exploitation between males for females.     

Reproductive success of parasitized males in a marine reef fish

Parasitism is hypothesized to reduce reproductive success in heavily parasitized males because females may preferentially mate with less parasitized males (parasite-mediated sexual selection) or parasites may compromise male competitiveness. In marine systems, this hypothesis is largely unexplored. This paper provides the first confirmed record of a copepod ectoparasite (Caligus buechlerae Hewitt 1964) on the common triplefin (Forsterygion lapillum) and evaluates the hypothesis that males parasitized with C. buechlerae experience lower reproductive success than unparasitized males (as determined by the presence and area of eggs within male nests). We found that 38 % of males we surveyed were infected with at least one C. buechlerae, with a median of two individuals per infected male. About 32 % of males were defending eggs, with 62.5 % of those males infected with at least one parasite. Males of greater total length (TL) were both more likely to be infected and more likely to be defending eggs. However, when statistically accounting for the effects of TL, parasite infection had no effect on the probability of defending eggs, or the average surface area of eggs when present. Positive covariation in fish length, the presence of eggs and parasite infection observed here potentially suggest that the importance of parasitic infection on reproductive success may depend upon the strength of selection for larger male body size. Our study is one of the few studies to investigate the effects of ectoparasites on reproductive success in reef fish and also provides a quantitative measure of infection for a widespread species within New Zealand.     

The energetic cost of protogynous versus protandrous sex change in the bi-directional sex-changing fish Gobiodon histrio

To investigate the relative cost of protogynous versus protandrous sex change we induced sex change in each direction in Gobiodon histrio (Gobiidae) and then compared growth, body condition and biochemical condition between sex-changed and non-sex-changed fish in treatment and control groups. Sex change in each direction was induced by establishing pairs of adult males and pairs of adult females on isolated coral colonies. Heterosexual pairs were used as controls. For both males and females, growth and body condition did not vary between fish that changed sex and those that did not. The relatively low cost of sex change, compared to the likely costs of searching for a mate of the correct sex, appears to explain the evolution of bi-directional sex change in coral-dwelling gobies. Lipid concentrations in the liver of males and females that changed sex were reduced by similar amounts (34% and 41%, respectively) compared to male and female controls that did not change sex. Therefore, changes in biochemical condition were approximately equal for fish that sex change in each direction and cannot explain the unequal frequency of sex change in each direction in natural populations of G. histrio.     

Testosterone treatment suppresses paternal care in superb fairy-wrens, Malurus cyaneus, despite their concurrent investment in courtship

Courtship displays and paternal care in male birds are generally thought to be mutually exclusive, because testosterone, necessary for stimulation of sexual behaviours, suppresses paternal behaviours. Superb fairy-wrens, Malurus cyaneus, are unusual in that males concurrently engage in courtship and paternal care. Fairy-wrens live in stable socially monogamous pairs with 0-4 subordinate male helpers. Both helper and dominant males provide care whenever it is required but continue courtship throughout the period of care as most fertilisations are extra-group and females are multi-brooded. To examine the role of testosterone in this trade-off, we compared testosterone levels in males of different social status, while they had dependent nestlings, and determined the effect of testosterone treatment on provisioning rates of pairs. Testosterone levels were lower in subordinate helpers, although these do not provide more paternal care than dominant males. Conversely, testosterone levels were similar in dominant males with or without helpers, although as the number of helpers increases males invest substantially less in nestling care and more in extra-group courtship. Although testosterone levels are high, irrespective of paternal duties, experimental testosterone treatment of males resulted in a large (65%) reduction in nestling feeding rates. Surprisingly, there was no indication that females compensated for this reduction in provisioning, suggesting that females might assume a constant male contribution to offspring care. We conclude that during nestling provisioning, male fairy-wrens maintain testosterone at an individual level that does not interfere with parental duties, while allowing high investment in extra-group courtship.     

The effects of parasites on male ornaments and female choice in the lek-breeding black grouse (Tetrao tetrix)

Summary We describe the results of two studies of parasitic infection in the black grouse (Tetrao tetrix). The first deals with our own observations of lekking black grouse in which the parasite levels of two blood parasites, the protozoan Leucocytozoon lovati and microfilaria, probably produced by a nematode worm Splendidofilaria tuvensis, were scored. We also obtained measures of age, survival, number of copulations, body mass and length of the ornamental tail feathers (the lyre) of the lekking males. The second study analysed the data from Lund (1954) which involved eight gut parasites obtained from birds which were killed. In the first study we found higher levels of infection of Leucocytozoon in adults relative to young birds. Parasites had no effect on male survival and there was no correlation in infection between the two types of parasites. Birds infected with microfilaria had shorter tail ornaments. There was no relationship between parasitic infection and mating success. However, the data indicated that such a trend indeed may exist for Leucocytozoon and the most successful males on the leks were less often infected by Leucocytozoon than other males. Results of the second study showed a negative relationship between parasite load (a combined measure of all parasites) and both ornamental tail feather length and body mass. These observations are compatible with, but not conclusive evidence for, the hypothesis of Hamilton and Zuk (1982) on the evolution of secondary sexual characters, where females choose to mate with genetically resistant males which show their resistance by expressing larger and more showy secondary sexual characters. Alternative explanations for the observed patterns are: females avoid infected males for some immediate benefit; and/or parasite loads are indicators of general stress rather than genetical resistance. Under the latter hypothesis females could mate with more vigorous males for reasons unrelated to parasite resistance.     

The economics of harem maintenance in the sac-winged bat, Saccopteryx bilineata (Emballonuridae)

Saccopteryx bilineata has a polygynous mating system in which males defend females in a harem territory. Harem defense and courtship include energetically costly flight maneuvers and hovering displays. We tested if (1) harem males have a greater field metabolic rate than non-harem males or females and if (2) the field metabolic rate of harem males is correlated with the number of females in a harem territory. We measured the energy budget in 32 S. bilineata with the doubly labeled water method and compared these estimates with behavioral observations in the daytime roost. Among adult bats, field metabolic rate varied with body mass by an exponent of approximately two. We found no significant difference in field metabolic rate or mass-specific field metabolic rate between harem and non-harem males. The mass-specific field metabolic rate of harem-males increased with harem size. The latter finding supports the hypothesis that the energy costs of courtship display and territorial defense influence the energy budget of harem males. Overall, field metabolic rates of S. bilineata were lower than those of similarly sized bats of the temperate zone and only 2.3 times above the basal metabolic rate recorded for this species. We suggest that male S. bilineata did not take advantage of their metabolic capacity because a prudent allocation of energy to activities of harem maintenance is an adaptive strategy for males in this mating system.     

Quinones in cockchafers: additional function of a sex attractant as an antimicrobial agent

Summary. Females of the forest cockchafer, Melolontha hippocastani Fabr. (Coleoptera: Scarabaeidae, Melolonthinae), are known to produce toluquinone and 1,4-benzoquinone. The latter component has been shown in our earlier studies to act as a sex attractant that enhances synergistically the attraction of males towards plant volatiles induced by feeding females. Analyses of whole body extracts from adults and grubs (L3) of M. hippocastani by coupled gas chromatography--mass spectrometry revealed the presence of 1,4-benzoquinone and toluquinone also in males and larvae. Quantitative analyses showed that extracts from females contained significantly more of 1,4-benzoquinone and toluquinone than extracts from males. Remarkably, extracts from grubs contained significantly higher amounts of both compounds than extracts from females. Inhibition assays using Escherichia coli, Saccharomyces cerevisiae, and the entomopathogenic fungi Metarhizium anisopliae and Beauveria brongniartii revealed inhibitory effects of 1,4-benzoquinone and toluquinone against all tested microorganisms. However, the amounts necessary for inhibition of entomopathogenic fungi and S. cerevisiae in the laboratory assay were higher than those found in the extracts from M. hippocastani.     

Client preferences by Caribbean cleaning gobies: food,safety or something else?

Predation risk is amongst the most pervasive selective pressures influencing behaviour and animals have been repeatedly shown to trade-off foraging success for safety. We examined the nature of this trade-off in cleaning symbioses amongst Caribbean coral reef fishes. We predicted that cleaning gobies (Elacatinus evelynae and Elacatinus prochilos) should prefer fish clients that pose a low risk of predation (e.g. herbivores) over clients that may have more ectoparasites but pose a higher risk (e.g. piscivores). Our field observations revealed that cleaners did clean preferentially client species with more parasites but predatory and non-predatory clients had similar ectoparasite loads. Despite the lack of a foraging advantage for inspecting predators, cleaners did not avoid risky clients. On the contrary, a larger proportion of visiting predators than non-predators was inspected, gobies initiated more interactions with predatory clients, and predators were attended to immediately upon arrival at cleaning stations. This preferential treatment of dangerous clients may allow the rapid identification of cleaners as non-prey item or may be due to the effect of predators on the rest of the cleaners’ clientele, which avoided cleaning stations whilst predators were present. Dealing with potentially risky clients may allow gobies to regain access to their main food source: non-predatory clients.     

Dual function of allopreening in the cooperatively breeding green woodhoopoe, Phoeniculus purpureus

Allopreening is a widespread but little-studied phenomenon in birds and is particularly prevalent in species where individuals are forced into close proximity. Such a situation facilitates the transfer of ectoparasites between individuals and allopreening has therefore been proposed to serve a hygienic function. In addition, allopreening might theoretically play a role in social communication. Green woodhoopoes (Phoeniculus purpureus) are cooperatively breeding birds that roost communally every night in a tree cavity and are thus susceptible to high ectoparasite loads. Our results suggest that allopreening of the head and neck (“head”), which cannot be efficiently self-preened, serves a primarily hygienic function: all individuals, irrespective of sex, dominance status, and group size, donated and received similar rates of head allopreening and terminated a similar proportion of bouts in which they were involved. Furthermore, there was a high occurrence of reciprocation and head allopreening occurred at a constant rate throughout the year. In contrast, allopreening of the rest of the body, which is accessible to the recipient itself, is likely to serve a primarily social function: body allopreening rates were higher in larger groups; dominant individuals received more body allopreening and terminated a significantly higher proportion of bouts than subordinates; and subordinates donated body allopreening at a higher rate than dominants. Moreover, bouts initiated by dominants were more likely to be reciprocated than those initiated by subordinates and body allopreening rates varied seasonally. Allopreening in the green woodhoopoe is therefore likely to serve a dual function, depending on the part of the body involved.     

The phalloid organ, orgasm and sperm competition in a polygynandrous bird: the red-billed buffalo weaver (Bubalornis niger)

The buffalo weavers, Bubalornis spp., are unique amongst birds in possessing a phalloid organ, a phallus-like structure anterior to the cloaca. We studied the red-billed buffalo weaver Bubalornis niger, to determine whether the phalloid organ has evolved in response to sperm competition. The phalloid organ was significantly longer in males that were resident at nests than in non-resident males, and among resident males was significantly longer in those males with a harem than in those without. Red-billed buffalo weavers bred colonially and had either a cooperatively polygynandrous (usually two unrelated males and several females) or a polygynous (one male and several females) mating system. Cooperative polygynandry provided females with the opportunity to copulate with more than one male and paternity analyses using DNA fingerprinting revealed that 63% of 16 multiple-offspring broods, comprising 43 offspring, had multiple sires, which included both nest-owning males and extra-group males. Sperm competition was therefore intense. Observations and experiments with buffalo weavers in captivity revealed that the phalloid organ was not intromittent during copulation, but functioned as a stimulatory organ which necessitated protracted copulation in order to induce male 'orgasm' and ejaculation, a feature apparently unique to this species.     

No reason to sneak: why males of all sizes can breed in the hole-nesting blenny, Aidablennius sphinx

Most blennioid fishes show a resource-based, promiscuous mating system with alternative 'sneaking' mating tactics. The hole-nesting species, Aidablennius sphinx, however, appears to be an exception; small males did not mimic females, most had their own nest and not once in 20 h of spawning observations did a second male enter a nest. In this field study, we ask if sneaker tactics are constrained and what factors favour independent nesting by small males. Larger males received more eggs sooner and attracted more females than smaller males. Larger males may be preferred because they released more sperm per ejaculation and fanned their eggs more often. In the long-term, however, larger males did not spawn more often than smaller males since: (1) the nests of large males filled up with eggs sooner than the nests of small males; (2) large males refused females more often than small males; and (3) a highly biased ratio of females to preferred large males meant many females had no option but to spawn with small males. Thus, small males nest independently, despite potential for female mimicry tactics (multiple females spawned simultaneously) and simultaneous parasitic spawning (males exited the nest during spawning)     

Testosterone and the allocation of reproductive effort in male house finches (Carpodacus mexicanus)

Testosterone has been proposed to serve as the mediator that controls the relative effort that an individual male bird will devote to mating effort versus parental effort. Here, we demonstrate a testosterone-influenced trade-off between parental and mating efforts in male house finches. Male house finches with experimentally elevated testosterone fed nestlings at a significantly lower rate, but sang at a higher rate than males without manipulated testosterone levels. Females mated to testosterone-implanted males fed nestlings at a significantly higher rate than females mated to males without testosterone implants, resulting in similar feeding rates for both treated and untreated pairs. The effects of testosterone on male house finches, however, were not as dramatic as the effects of testosterone observed in some other socially monogamous species of birds. Because extra-pair copulations are uncommon in house finches and males provide substantial amounts of parental care, these more modest effects may be due to differences in how the allocation of reproductive effort affects the costs and benefits of different reproductive behaviors. Received: 6 June 2000 / Accepted: 17 July 2000     

Love thy neighbour? Social nesting pattern,host mass and nest size affect ectoparasite intensity in Darwin’s tree finches

Social nesting behaviour is commonly associated with high prevalence and intensity of parasites in intraspecific comparisons. Little is known about the effects of interspecific host breeding density for parasite intensity in generalist host–parasite systems. Darwin’s small tree finch (Camarhynchus parvulus) on Santa Cruz Island, Galápagos Islands, nests in both heterospecific aggregations and at solitary sites. All Darwin finch species on Santa Cruz Island are infested with larvae of the invasive blood-sucking fly Philornis downsi. In this study, we test the prediction that total P. downsi intensity (the number of parasites per nest) is higher for nests in heterospecific aggregations than at solitary nests. We also examine variation in P. downsi intensity in relation to three predictor variables: (1) nest size, (2) nest bottom thickness and (3) host adult body mass, both within and across finch species. The results show that (1) total P. downsi intensity was significantly higher for small tree finch nests with many close neighbours; (2) finches with increased adult body mass built larger nests (inter- and intraspecific comparison); (3) parasite intensity increased significantly with nest size across species and in the small tree finch alone; and (4) nest bottom thickness did not vary with nest size or parasite intensity. These results provide evidence for an interaction between social nesting behaviour, nest characteristics and host mass that influences the distribution and potential impact of mobile ectoparasites in birds.     

Female behaviour mediates male courtship under predation risk in the guppy (Poecilia reticulata)

Previous work has shown that under elevated predation risk, male guppies (Poecilia reticulata) switch from courtship to less conspicuous coercive mating attempts. This behavioural transition is traditionally interpreted as a 'risk-sensitive' response that makes males less conspicuous to predators. However, predation risk leads to behavioural changes (such as schooling and predator inspection) in females that may result in coercive mating attempts being more profitable in high-risk situations. Here, we tested the hypothesis that the switch to coercive mating by male guppies in high-risk situations is mediated by adjustments in female behaviour, rather than directly by the predator. We used replicate models resembling a known guppy predator to simulate predation risk in wild-caught guppies from a high-predation population in Trinidad. Our results revealed that males performed proportionately more coercive mating attempts when presented with a female that had been exposed previously to a model predator compared to when males were paired with non-exposed females. Total mating activity (combined rates of courtship and forced mating attempts) did not differ significantly among the two treatment groups, indicating that overall mating activity is unaffected by predation risk. Importantly, when we subsequently presented both sexes concurrently with a predator model, total mating activity and the proportion of forced mating attempts remained unchanged in the high-risk treatment. Taken together, these results indicate that the transition from courtship to forced mating attempts under elevated predation risk is mediated by changes in female behaviour, which we suggest may favour the use of coercive mating under high predation risk.     

Experimental evidence of a testosterone-induced shift from paternal to mating behaviour in a facultatively polygynous songbird

Previous studies have suggested that testosterone (T) profiles of male birds reflect a trade-off between mate attraction behaviours (requiring high T levels) and parental care activities (requiring low T levels). In this study, we experimentally elevated T levels of monogamous males in the facultatively polygynous European starling (Sturnus vulgaris), and compared mate attraction and paternal behaviour of T-treated males with those of controls (C-males). T-males significantly reduced their participation in incubation and fed nestlings significantly less often than C-males. Females paired to T-treated males did not compensate for their mate’s lower paternal effort. The observed reduction in a male’s investment in incubating the eggs was accompanied by an increased investment in typical female-attracting behaviours: T-males spent a significantly higher proportion of their time singing to attract additional females. They also occupied more additional nestboxes than C-males, although the differences just failed to be significant, and carried significantly more green nesting materials into an additional nestbox (a behaviour previously shown to serve a courtship function). T-males also behaved significantly more aggressively than C-males. During the nestling period, the frequency of mate-attracting behaviours by T-treated and control males no longer differed significantly. Despite the reduced paternal effort by T-males and the lack of compensation behaviour by females, hatching and breeding success did not differ significantly between T- and C-pairs. Received: 7 February 2000 / Revised: 10 August 2000 / Accepted: 3 September 2000     

Sexual selection and species recognition in the pygmy swordtail, Xiphophorus pygmaeus: conflicting preferences

Sexual selection and species recognition play important roles in mate choice; however, sexual selection preferences may overlap with traits found in heterospecifics, producing a conflict between sexual selection and species recognition. We examined female preferences in Xiphophorus pygmaeus for male traits that could provide both types of information to determine how females use multiple cues when preferences for these cues would conflict. We also examined X. pygmaeus behavior in the field to determine if females have the opportunity to choose mates. As no male-male competition was observed in the field, and females occasionally chased males from feeding areas, females apparently have the opportunity to exercise mate choice in their natural habitat. In the laboratory, female X. pygmaeus used body size as a sexual selection cue, preferring large heterospecifics (X. cortezi) to small conspecifics. Females also preferred barless X. cortezi over barred X. cortezi when males were size matched. Because X. pygmaeus males do not have bars, this preference suggests that X. pygmaeus females use vertical bars in species recognition, and that large body size and vertical bars are conflicting cues. However, X. pygmaeus females did not have a preference for males of either species when sexual selection and species recognition cues were presented concurrently. This result was surprising, because preferences for species recognition cues are often assumed to be stronger than sexual selection cues. We suggest that females may be using additional species-specific cues in mate choice to prevent hybridization.