Misleading mollies: surface- but not cave-dwelling Poecilia mexicana males deceive competitors about mating preferences

Individuals providing misleading information to conspecifics may benefit from deception at the receiver's expense. A recent study (Plath et al., Curr Biol 18:1138–1141, 2008c) suggested that male Atlantic mollies (Poecilia mexicana) deceive rival males about their preferred mate. Here, we contrasted potentially deceptive behavior in surface-dwelling P. mexicana males to males of the cave form of that species (the cave molly). Unlike many other cavefishes, cave mollies have retained functional eyes and readily respond to visual stimuli. Males could interact freely with two females (large and small), and an audience male was visually presented during the second part of the tests. When observed during mate choice, males reduced their mating activity, but this reduction was significantly weaker in cave mollies. Overall, the expression of mating preferences (determined through frequencies of nipping and thrusting) declined in front of an audience; again, this effect was significantly weaker in the cave form. Reduced sexual activity and reduced expression of mating preferences can be interpreted as an attempt of the focal male to avoid unintended interception of information by the rival male. Surface but not cave molly males directed their first sexual interaction (when being observed by the rival male) towards the initially non-preferred female, suggesting that surface-dwelling males deceive rival males about their mating preferences. Deception by the focal males may be an adaptation to avoid sperm competition, since other males in their social environment may use public information and copy the focal male's mate choice. It seems that sending deceptive signals is evolutionarily regressed in the cave molly, since mate choice copying is unlikely to occur under naturally dark conditions, and also the potential to deceive rivals about mating preferences is probably very limited.     

Sex recognition in surface- and cave-dwelling Atlantic molly females (<Emphasis Type=Italic>Poecilia mexicana</Emphasis>, Poeciliidae,Teleostei): influence of visual and non-visual cues

Cave fishes need to rely on non-visual senses, such as the sense of smell or the lateral line to communicate in darkness. In the present study, we investigated sex identification by females of a cave-dwelling livebearing fish, Poecilia mexicana (cave molly), as well as its surface-dwelling relatives. Unlike many other cave fishes, cave mollies still possess functional eyes. Three different modes of presentation of the stimulus fish (a male and an equally sized female) were used: (i) the stimulus fish were presented behind wire-mesh in light, allowing the focal female to perceive multiple cues, (ii) the experiment was carried out under infrared conditions, such that only non-visual cues could be perceived and (iii) the stimulus fish were presented in light behind transparent Plexiglas, allowing for the use of visual cues only. Females of all populations examined preferred to associate with the stimulus female in at least one of the treatments, but only when visible light was provided, suggesting that far-range sex recognition is limited or even absent in the cave molly under naturally dark conditions.     

Size-dependent male mating behaviour and sexual harassment in a population of Atlantic mollies (Poecilia mexicana) from a sulphur creek

The Atlantic molly Poecilia mexicana inhabits a variety of habitats. In previous studies, small males from clear-water populations showed considerably more sexual behaviours than large males. Males from a sulphur creek, the El Azufre, or from a sulphur cave (cave molly) showed comparatively low sexual activity, and typical size-dependent mating behaviour was either absent or large males showed even more sexual behaviour than smaller ones. Sexually deprived cave molly males increased their sexual activity, but small males still did not show more sexual behaviour than large ones, suggesting that the genetic basis for typical size-dependent mating behaviour has been lost. Likely, the extreme abiotic conditions (hypoxia and toxic hydrogen sulphide) have selected against energetically costly behaviours. In this paper, we examined how El Azufre males would respond to sexual deprivation. We found these males to also increase their sexual activity after sexual deprivation but, unlike cave mollies, small males now showed more sexual behaviour than large ones, suggesting that the genetic basis for this behaviour is not lost in this population. Differences between populations may be due to the less harsh characteristics of El Azufre (e.g. less H₂S), resulting in weaker selection against energy-consuming behaviours. Furthermore, we tested for potential costs of male sexual harassment for females in terms of reduced feeding efficiency in the presence of a male, as was shown for P. mexicana from a clear-water population, but was not found in cave mollies or the El Azufre fish. Test females were either starved for 1 week to increase hunger levels or male sexual deprivation and female starvation were combined; however, we found no evidence for male sexual harassment even after these treatments. Our results parallel previous findings in the cave molly and suggest that El Azufre males have lost specific behavioural traits that cause sexual harassment.     

Maternal effects, conspecific chemical cues, and switching from parthenogenesis to gametogenesis in the cladoceran Moina macrocopa

The change in reproductive mode from parthenogenesis to gametogenesis in Cladocera is controlled by multiple environmental cues. Maternal effects are involved in the control of reproductive switching. In this study, we estimated the readiness of Moina macrocopa females to change reproduction mode under the effect of conspecific chemicals on maternal and offspring generations. The results demonstrated that information about the chemical environment was not transmitted between generations (none of the females produced diapausing eggs in the control medium irrespective of their mothers' environment). Differences in maternal energetic investments were not significant, hence the maternal environment did not affect the fecundity. However, tested animals adapted to the effect of the diapause inducing factor. When offspring of mothers cultured in crowded water were also cultured in crowded water (the constant effect of conspecific chemicals), they switched less readily to gametogenesis than offsprings of mothers cultured in fresh medium.     

Lack of species discrimination based on chemical cues by male sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>

When making mating decisions, individuals may rely on multiple cues from either the same or multiple sensory modalities. Although the use of visual cues in sexual selection is well studied, fewer studies have examined the role of chemical cues in mate choice. In addition, few studies have examined how visual and/or chemical cues affect male mating decisions. Male mate choice is important in systems where males must avoid mating with heterospecific females, as is found in a mating complex of Poecilia. Male sailfin mollies, Poecilia latipinna, are sexually parasitized by gynogenetic Amazon mollies, P. formosa. Little is known about the mechanism by which male sailfin mollies base their mating decisions. Here we tested the hypothesis that male sailfin mollies from an allopatric and a sympatric population with Amazon mollies use multiple cues to distinguish between conspecific and heterospecific females. We found that male sailfin mollies recognized the chemical cues of conspecific females, but we found no support for the hypothesis that chemical cues are by themselves sufficient for species discrimination. Lack of discrimination based on chemical cues alone may be due to the close evolutionary history between P. latipinna and P. formosa. Males from populations sympatric with Amazon mollies did not differentially associate with females of either of the two species when given access to both visual and chemical cues of the females, yet males from the allopatric population did associate more with conspecific females than with heterospecific females in the presence of both chemical and visual cues. The lack of discrimination by males from the sympatric population between conspecific and heterospecific females based on both chemical and visual cues suggests that these males require more complex combinations of cues to distinguish species, possibly due to the close relatedness of these species.     

Parallel evolution leads to reduced shoaling behavior in two cave dwelling populations of Atlantic mollies (<Emphasis Type=Italic>Poecilia mexicana</Emphasis>, Poeciliidae,Teleostei)

Shoaling behavior protects fishes from avian and piscine predation, but at the same time costs of group living arise due to several mechanisms including increased food competition. Most cave fishes live in an environment in which avian and piscine predators are lacking, and cave environments are often characterized by low food availability, leading to increased food competition. Altogether, this should favor the reduction of shoaling in cave fishes. We compared shoaling behavior (i.e. the tendency to associate with a stimulus shoal) among surface dwelling populations of the Atlantic molly, Poecilia mexicana, and two cave forms of that species. The first cave population of P. mexicana originated from the Cueva del Azufre and was previously recognized as the only cave form of a poeciliid fish. The second cave population examined came from a cave that was discovered only recently (Cueva Luna Azufre). In both cave forms shoaling behavior was reduced compared with surface dwelling mollies.     

Physiological responses to hyper-saline waters in sailfin mollies (Poecilia latipinna)

We examined the ionoregulatory physiology and biochemistry of the teleost sailfin molly (Poecilia latipinna), an inhabitant of salt marshes along the gulf coast, during exposure to hyper-saline waters (salinity range 35-95 ppt). Mollies were able to tightly control plasma Na(+) and Cl(-) concentrations and tissue water levels up to 65 ppt, but at higher salinities plasma ion levels began to rise and muscle water content dropped. Still, even at the highest salinity (90 ppt) plasma Na(+) and Cl(-) levels were only 32% and 39%, respectively, above levels at 35 ppt. Drinking rates at 60 ppt climbed 35%, while gut Na(+)/K(+)-ATPase (NAK) activity rose 70% and branchial NAK activity jumped 200%. The relatively small rise in drinking rate, in the face of a more than doubling of the osmotic gradient, suggests that a reduction in branchial water permeability significantly limited water loss and associated salt load. At 80 ppt, a salinity where plasma ion levels just begin to rise, drinking rate rose more rapidly, but gut and gill NAK activity did not, suggesting that mollies employed other pathways (perhaps renal) of salt excretion. At higher salinities, plasma ion levels continued to rise and muscle water content fell slightly indicating the beginnings of internal osmotic disturbances. To evaluate the energetic costs of hyper-salinity on mollies we measured the rate of O(2) consumption and found it rose with salinity, in sharp contrast to virtually all species previously examined. Interestingly, despite higher metabolism, growth was unaffected by hyper-salinity.     

Chemical cues related to conspecific size in pintado catfish, Pseudoplatystoma coruscans

The pintado (Pseudoplatystoma coruscans) is a ferocious carnivorous catfish with evident cannibalistic behaviour; its nocturnal habits are related to its ability to use predominately chemical sensorial modalities. This study investigated whether the pintado distinguishes conspecifics of different body sizes using chemical cues, which may reflect different physiological conditions such as hunger or stress. Pintados were observed when receiving water conditioned by either larger or similar-size conspecifics. A control group consisted of pintados receiving unconditioned water. Twelve repetitions were used for each condition. Feeding-like behaviours were investigated in the receiver fish and showed that they responded only to the conditioned water. Furthermore, a higher frequency of responses occurred when the water was conditioned by a similar-size conspecific. Thus, it is concluded that pintados are able to recognize conspecific size by chemical cues related to size and that this ability contributes to the individual's decision making on whether to approach or to avoid the conspecific.     

Aggregate formation in a freshwater bacterial strain induced by growth state and conspecific chemical cues

We investigated the induction of aggregate formation in the freshwater bacterium Sphingobium sp. strain Z007 by growth state and protistan grazing. Dialysis bag batch culture experiments were conducted in which these bacteria were grown spatially separated from bacteria or from co‐cultures of bacteria and predators. In pure cultures of Sphingobium sp. strain Z007, the concentrations of single cells and aggregates inside and outside the dialysis membranes developed in a similar manner over 3 days of incubation, and the proportions of aggregates were highest during the exponential growth phase. Cell production of Sphingobium sp. strain Z007 was enhanced in the presence of another isolate, Limnohabitans planktonicus, from an abundant freshwater lineage (R‐BT065) outside the bags, and even more so if that strain was additionally grazed upon by the bacterivorous flagellate Poterioochromonas sp. However, the ratios of single cells to aggregates of Sphingobium sp. strain Z007 were not affected in either case. By contrast, the feeding of flagellates on Sphingobium sp. strain Z007 outside the dialysis bags led to significantly higher proportions of aggregates inside the bags. This was not paralleled by an increase in growth rates, and all cultures were in a comparable growth state at the end of the experiment. We conclude that two mechanisms, growth state and the possible release of infochemicals by the predator, may induce aggregate formation of Sphingobium sp. strain Z007. Moreover, these infochemicals only appeared to be generated by predation on cells from the same species.     

Public information for solitary foragers: timber rattlesnakes use conspecific chemical cues to select ambush sites

Many animals use public information (PI) gathered from conspecificsto assess the quality of potential foraging locations. To date,research on this phenomenon has focused almost exclusively onsocial foragers that live in groups and monitor nearby individuals.PI is potentially available to solitary foragers as well, inthe form of cues (such as chemical cues) that persist in theenvironment after conspecifics are no longer present. In thisstudy, I examined the response of a solitary sit-and-wait predator,the timber rattlesnake (Crotalus horridus), to chemical cuesfrom conspecifics that had recently fed as opposed to thosethat had been deprived of food. Experiments with a T-maze indicatedthat timber rattlesnakes always follow conspecific chemicaltrails out of the maze, regardless of whether or not the individualleaving the trail had recently fed. However, an enclosure choicetest found that individuals are more likely to select ambushsites in areas with chemical cues from conspecifics that hadrecently fed. These results indicate that snakes may use conspecificchemical cues not only to find mates, shelter sites, and hibernaculabut also profitable food patches. Additionally, this study highlightsthe possibility that other solitary foragers may use PI to guidetheir foraging behavior.     

Pigments and ultrastructures of pigment cells in xanthic sailfin mollies (Poecilia latipinna).

Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids.     

Geographical variation of genetic and phenotypic traits in the Mexican sailfin mollies, Poecilia velifera and P. petenensis

Comparing the patterns of population divergence using both neutral genetic and phenotypic traits provides an opportunity to examine the relative importance of evolutionary mechanisms in shaping population differences. We used microsatellite markers to examine population genetic structure in the Mexican sailfin mollies Poecilia velifera and P. petenensis. We compared patterns of genetic structure and divergence to that in two types of phenotypic traits: morphological characters and mating behaviours. Populations within each species were genetically distinct, and conformed to a model of isolation by distance, with populations within different geographical regions being more genetically similar to one another than were populations from different regions. Bayesian clustering and barrier analyses provided additional support for population separation, especially between geographical regions. In contrast, none of the phenotypic traits showed any type of geographical pattern, and population divergence in these traits was uncorrelated with that found in neutral markers. There was also a weaker pattern of regional differences among geographical regions compared to neutral genetic divergence. These results suggest that while divergence in neutral traits is likely a product of population history and genetic drift, phenotypic divergence is governed by different mechanisms, such as natural and sexual selection, and arises at spatial scales independent from those of neutral markers.     

Cytogenetics of bisexual/unisexual species of Poecilia. II. Analysis of heterochromatin and nucleolar organizer regions in Poecilia mexicana mexicana by C-banding and DAPI, quinacrine, chromomycin A3, and silver staining.

Chromosomes of Poecilia mexicana mexicana, one of the bisexual species involved in the hybrid origin of the unisexual teleost fish species P. formosa, were analyzed by several staining techniques. Sex-specific, differential heterochromatin, found in other congeneric species, was not observed in P. m. mexicana. Nucleolar organizer regions were polymorphic among individual specimens within a given population sample. A single specimen exhibiting intraindividual variability of chromosome pair 1 and a specimen with a triploid karyotype are also described.     

Influence of male competition on male mating behaviour in the cave molly, Poecilia mexicana

In many species, male mating behaviour is correlated with male body size, with large males often being preferred by females. Small surface-dwelling Poecilia mexicana males compensate for this disadvantage by being more sexually active and using sneaky copulations. In a cave-dwelling population, however, small males do not show this behaviour. Do small males alter their behaviour in the presence of a large rival? Here, we investigated the influence of male competition on male mating behaviour in the cave form. Two males of different sizes were mated with a female either alone or together with the other male. No aggressive interactions were observed between either fish. There was no statistically significant difference in the frequency of sexual behaviours between the two treatments. In both treatments, large males were more sexually active than small males. Thus, small cave molly males do not switch to an alternative mating behaviour in the presence of a larger rival. Possibly, the extreme environmental conditions in the cave (e.g. low oxygen content and high levels of hydrogen sulphide) favour saving energetic costs, resulting in the absence of alternative mating behaviour in small males.     

Visual and auditory cues in conspecific discrimination learning in Bengalese finches

Four Bengalese finches were trained to discriminate 2 conspecific individuals in an operant chamber. Still visual images and contact calls were simultaneously presented to the subjects and specific (“correct”) perching response was reinforced with food. After the birds acquired the discrimination, they received the first test in which visual cues alone, auditory cues alone and combination of the 2 modalities were presented. Visual cues dominantly controlled the discriminative behavior of all birds. Then the subjects received the second test in which mixtures of the visual image of 2 stimulus birds appeared under 3 different auditory conditions, namely, no call, calls of 1 bird and calls of the other bird. Two subjects used the auditory cues when the visual stimulus was a mixture of 2 stimulus birds. These results suggest that the birds used less dominant cues when the dominant cues gave ambiguous information.     

Inducible reproductive plasticity of the guppy Poecilia reticulata in response to predation cues

Predation has long been described as one of the major driving forces in evolution. Guppies (Poecilia reticulata) from natural populations exposed to different predation pressures, were found to have different life history traits. Reproductive plasticity in response to direct predation cues has mainly been reported for invertebrates. The goals of the present study were to determine whether exposure to predation cues would induce reproductive phenotypic plasticity in female guppies and to determine whether the effective cues are visual, chemical, or a combination of both. In our first experiment, female guppies exposed to predation cues of the african cichlids Aulonocara nyassae increased their reproductive output by almost two fold, having larger brood-sizes and shorter brood-interval at the first spawn. This effect disappeared in the second spawn in the absence of predators. In the second experiment we found that exposure to the predators induced an increase in the brood-size regardless of whether the cue was: only visual, only chemical, visual and chemical or visual, chemical and tactile. The impacts of these cues were equally powerful on the tested variables and they did not have any cumulative effect. Similar to the results of the first experiment, this effect disappeared in the second spawn, in the absence of predation cues. The present study demonstrates a direct immediate and reversible effect of predation cues on guppy reproduction.     

Behavioral response of juvenile silver and bighead carp to conspecific and heterospecific alarm cues

Biological Invasions - Predation is an important factor influencing the strength and success of a year class in many prey fishes. Many adaptations, including chemical cues, benefit shoaling groups...     

Sperm availability in naturally occurring bisexual-unisexual breeding complexes involvingPoecilia mexicana and the gynogenetic teleost,Poecilia formosa

Synopsis Testicular maturation indices (TMI) were determined for wild-caught males ofPoecilia mexicana by quantitative analysis of the frequency of ongoing stages of spermatogenesis and spermatid differentiation in sections of testes stained with the Feulgen reaction for DNA. In nature, males maintain essentially constant levels of sperm production throughout the year and show no significant variations in mean TMI values associated with season, microhabitat, standard body length, or rank in male dominance hierarchies. Winter males or males isolated from females in the laboratory show accumulation of mature spermatophores. These findings suggest that fluctuations in the microstructure of wild populations ofPoecilia from northeastern Mexico may be due primarily to differences in the temporal scheduling of female reproductive cycles and not to limitations imposed by sperm availability or male reproductive competence. The data are discussed in terms of competitive interactions within unisexual-bisexual breeding complexes involving the Amazon mollyP. formosa, its related triploid hybrids, and the bisexual species,P. mexicana.