Search

Since all forms of mimicry are based on perceptual deception, the sensory ecology of the intended receiver is of paramount importance to test the necessary precondition for mimicry to occur, that is, model‐mimic misidentification, and to gain insight in the origin and evolutionary trajectory of the signals. Here we test the potential for aggressive mimicry by a group of coral reef fishes, the color polymorphic Hypoplectrus hamlets, from the point of view of their most common prey, small epibenthic gobies and mysid shrimp. We build visual models based on the visual pigments and spatial resolution of the prey, the underwater light spectrum and color reflectances of putative models and their hamlet mimics. Our results are consistent with one mimic‐model relationship between the butter hamlet H. unicolor and its model the butterflyfish Chaetodon capistratus but do not support a second proposed mimic‐model pair between the black hamlet H. nigricans and the dusky damselfish Stegastes adustus. We discuss our results in the context of color morphs divergence in the Hypoplectrus species radiation and suggest that aggressive mimicry in H. unicolor might have originated in the context of protective (Batesian) mimicry by the hamlet from its fish predators rather than aggressive mimicry driven by its prey., Hamlets are colour polymorphic reef fishes believed to be diverging by aggressive mimicking of one of a number of unrelated non‐predatory fishes. We study the visual system of the intended receiver of hamlets' mimicry, their prey, and test whether model‐mimic mis‐identification by the prey is likely to occur. We find that only one hamlet is likely to be an efficient mimic in the eyes of their prey but we observe that the mimic colour morph might in fact have evolved by Batesian mimicry first and only subsequently recruited for aggressive mimicry.

Little is known about long-term changes in coral reef fish communities. Here we present a new technique that leverages fish otoliths in reef sediments to reconstruct coral reef fish communities. We found over 5,400 otoliths in 169 modern and mid-Holocene bulk samples from Caribbean Panama and Dominican Republic mid-Holocene and modern reefs, demonstrating otoliths are abundant in reef sediments. With a specially-built reference collection, we were able to assign over 4,400 otoliths to one of 56 taxa (35 families) though mostly at genus and family level. Many otoliths were from juvenile fishes for which identification is challenging. Richness (by rarefaction) of otolith assemblages was slightly higher in modern than mid-Holocene reefs, but further analyses are required to elucidate the underlying causes. We compared the living fish communities, sampled using icthyocide, with the sediment otolith assemblages on four reefs finding the otolith assemblages faithfully capture the general composition of the living fish communities. Radiocarbon dating performed directly on the otoliths suggests that relatively little mixing of sediment layers particularly on actively accreting branching coral reefs. All otolith assemblages were strongly dominated by small, fast-turnover fish taxa and juvenile individuals, and our exploration on taxonomy, functional ecology and taphonomy lead us to the conclusion that intense predation is likely the most important process for otolith accumulation in reef sediments. We conclude that otolith assemblages in modern and fossil reef sediments can provide a powerful tool to explore ecological changes in reef fish communities over time and space.

An adaptive visual system is essential for organisms inhabiting new or changing light environments. The Panama Canal exhibits such variable environments due to its anthropogenic origin and current human activities. Within the Panama Canal, Lake Gatun harbours several exotic fish species including the invasive peacock bass (Cichla monoculus, Agassiz, 1831), a predatory Amazonian cichlid. In this research, through spectral measurements and molecular and physiological experiments, we studied the visual system of C. monoculus and its adapative capabilities. Our results suggest that (1) Lake Gatun is a highly variable environment where light transmission changes throughout the canal-waterway, and that (2) C. monoculus has several visual adaptations suited for this red-shifted light enviroment. C. monoculus filters short-wavelengths (∼400 nm) from the environment through their ocular media and they tune their visual sensitivities to the available light through opsin gene expression. More importantly, based on shifts in spectral sensitivities of photoreceptors alone, and on transcriptome analysis, C. monoculus exhibits extreme intraspecific variation in the use of vitamin A1/A2 chromophore in their photoreceptors. Fish living in turbid water had higher proportions of vitamin A2, shifting sensitivities to longer-wavelengths, than fish living in clear waters. Furthermore, we also found variation in retinal transcriptomes where fish from turbid and clear-waters exhibited differentially expressed genes that vary greatly in their function. We suggest this phenotypic plasticity has been key in C. monoculus’ invasion.

Diet choice in marine species is typically derived from indirect methods such as stomach contents and stable isotope analysis, while choice experiments in controlled laboratory settings are used to infer foraging decisions in the wild. However, these methods are limited in their capacity to make inferences about foraging decisions by predators in variable environments or recreate the array of factors (such as prey traits, predator condition, and environmental conditions) present in natural systems which may interact to affect diet decisions by predators. Recent work has provided evidence for selectivity in the invasive Indo-Pacific lionfish (Pterois volitans/miles) despite the predator's apparent opportunistic, generalist feeding behavior. We directly tested diet choice by presenting wild-caught lionfish with multi-species prey assemblages in field enclosures. We offered lionfish equal biomasses of prey species sharing similar prey traits that are both highly abundant on coral reefs and prevalent in the lionfish diet across the invaded range. We then applied compositional analyses to determine relative prey consumption given prey availability. We observed lionfish selectively foraging on prey and manifesting strong consistent preferences for one prey species. Additionally, we observed condition-dependent foraging behavior, as lionfish with higher body conditions were more likely to exhibit selective foraging behavior. Our findings provide direct evidence for diet choice in an invasive generalist species and highlight the importance of preserving the ecological complexity of natural ecosystems in choice experiments, particularly when investigating predator-prey interactions in complex environments.

Intrasexual selection on body coloration is thought to play an important role in the evolution of colour polymorphism, but its physiological underpinnings have received limited attention. In the colour polymorphic cichlid Neochromis omnicaeruleus, three fully sympatric female colour morphs— a plain morph (P) and two conspicuously coloured blotched morphs, black-and-white blotched (WB) and orange blotched (OB)—differ in agonistic behaviour. We compared routine metabolic rate (when females were housed in social isolation), short-term energetic costs of interacting with a same-colour rival housed in an adjacent transparent chamber and oxidative stress between the three female colour morphs. WB females had a lower routine metabolic rate compared with the other colour morphs. WB females also had a lower active metabolic rate during inter-female interactions than OB females, while OB females used more oxygen per unit aggressive act than the other two colour morphs. However, there were no consistent differences in oxidative stress between the three morphs. Concerted divergence in colour, behaviour and metabolism might contribute to the evolution of these polymorphisms in sympatry.

Interest in the evolution of female ornaments has been growing but explaining their presence remains a challenge for many animal taxa. Although female ornaments may be sexually selected via male choice, they can also function in female–female competition. Here, we studied a stream-resident population of three-spined sticklebacks (Gasterosteus aculeatus), in which females possess male-typical red throat coloration, and a nearby anadromous population that lacks such coloration and is thought to possess ancestral character states for most traits in this species complex. We asked first whether there were population-level differences in agonism that might be associated with the evolution of female ornaments. We tested if the derived population possessing some red-throated females exhibited relatively higher levels and clearer patterns of within-population aggression and dominance in dyadic trials and more frequent behavioral dominance over individuals of the population lacking red females. Second, to address the relationship between the derived coloration and female–female competition, we tested whether red-throated stream females were more aggressive and dominant toward dull-throated stream females in both dyadic and socially complex contexts. We found that clear dominance was established more often in pairs of stream females, and stream females were more often dominant in stream-anadromous dyads. However, we found no clear evidence that the red throat coloration was directly linked to a female competitive advantage within the stream population, suggesting alternative untested signaling or perhaps nonadaptive functions. Our study represents the first evaluation of the potential relationship between a male-typical nuptial trait and intrasexual competition in female three-spined sticklebacks.

Female color polymorphisms are common in the cichlid species radiations of Lake Victoria and Lake Malawi. According to theory, when a population harbors variation in sex-determining factors, polymorphism in female-linked coloration might generate individual variation in male mating preferences for female color morphs. We tested whether individual males exhibit consistent mating preferences for female color morphs in the Lake Malawi cichlid Pseudotropheus (Maylandia) 'zebra gold', a species polymorphic for female coloration and sex determination. We also explored whether male mating preferences could be predicted by maternal coloration or were acquired by imprinting on siblings' coloration. We found large individual variation in the strength and direction of male preferences for sex-linked female color patterns. Male mating preferences could be predicted by the mother's color morph and were not affected by visual imprinting. These findings represent the first evidence of male choice on sex-linked female coloration in a Lake Malawi cichlid. Our analysis indicates a strong genetic component to male preference for female coloration and large individual variation in the strength and direction of male mating preferences. Within-population variation in innate mating preferences might have important implications in cichlid fish species radiations. Copyright 2008, Oxford University Press.

Midas cichlid fish are a Central American species flock containing 13 described species that has been dated to only a few thousand years old, a historical timescale infrequently associated with speciation. Their radiation involved the colonization of several clear water crater lakes from two turbid great lakes. Therefore, Midas cichlids have been subjected to widely varying photic conditions during their radiation. Being a primary signal relay for information from the environment to the organism, the visual system is under continuing selective pressure and a prime organ system for accumulating adaptive changes during speciation, particularly in the case of dramatic shifts in photic conditions. Here, we characterize the full visual system of Midas cichlids at organismal and genetic levels, to determine what types of adaptive changes evolved within the short time span of their radiation. We show that Midas cichlids have a diverse visual system with unexpectedly high intra- and interspecific variation in color vision sensitivity and lens transmittance. Midas cichlid populations in the clear crater lakes have convergently evolved visual sensitivities shifted toward shorter wavelengths compared with the ancestral populations from the turbid great lakes. This divergence in sensitivity is driven by changes in chromophore usage, differential opsin expression, opsin coexpression, and to a lesser degree by opsin coding sequence variation. The visual system of Midas cichlids has the evolutionary capacity to rapidly integrate multiple adaptations to changing light environments. Our data may indicate that, in early stages of divergence, changes in opsin regulation could precede changes in opsin coding sequence evolution. published

The amount of short wavelength (ultraviolet (UV), violet and blue) light that reaches the retina depends on the transmittance properties of the ocular media, especially the lens, and varies greatly across species in all vertebrate groups studied previously. We measured the lens transmittance in 32 anuran amphibians with different habits, geographical distributions and phylogenetic positions and used them together with eye size and pupil shape to evaluate the relationship with diel activity pattern, elevation and latitude. We found an unusually high lens UV transmittance in the most basal species, and a cut-off range that extends into the visible spectrum for the rest of the sample, with lenses even absorbing violet light in some diurnal species. However, other diurnal frogs had lenses that transmit UV light like the nocturnal species. This unclear pattern in the segregation of ocular media transmittance and diel activity is shared with other vertebrates and is consistent with the absence of significant correlations in our statistical analyses. Although we did not detect a significant phylogenetic effect, closely related species tend to have similar transmittances, irrespective of whether they share the same diel pattern or not, suggesting that anuran ocular media transmittance properties might be related to phylogeny.

Female mating preferences can influence both intraspecific sexual selection and interspecific reproductive isolation, and have therefore been proposed to play a central role in speciation. Here, we investigate experimentally in the African cichlid fish Pundamilia nyererei if differences in male coloration between three para-allopatric populations (i.e. island populations with gene flow) of P. nyererei are predicted by differences in sexual selection by female mate choice between populations . Second, we investigate if female mating preferences are based on the same components of male coloration and go in the same direction when females choose among males of their own population, their own and other conspecific populations and a closely related para-allopatric sister-species, P. igneopinnis . Mate-choice experiments revealed that females of the three populations mated species-assortatively, that populations varied in their extent of population-assortative mating and that females chose among males of their own population based on different male colours. Females of different populations exerted directional intrapopulation sexual selection on different male colours, and these differences corresponded in two of the populations to the observed differences in male coloration between the populations. Our results suggest that differences in male coloration between populations of P. nyererei can be explained by divergent sexual selection and that population-assortative mating may directly result from intrapopulation sexual selection.

Theory predicts that males should tailor the size of their ejaculates according to temporal changes in the risk of sperm competition. Specifically, males are predicted to allocate more sperm to each mating event with increasing risk (i.e., the probability that the sperm from two males will compete for fertilization). We tested this hypothesis by using the eastern mosquitofish, a freshwater species of fish exhibiting a coercive mating system and internal fertilization. We manipulated the perception of sperm competition risk by adjusting the sex ratio under which males were maintained over 8 days. Males were housed either with three females and one male (simulating high sperm competition risk) or with four females (low risk). After the treatment, we presented each test male individually to an unfamiliar male-deprived female for 30 minutes and observed his mating behavior. We then artificially stripped the test males of sperm and recovered the ejaculates from the females. Our results revealed that males in the high-risk group performed higher levels of mating activity and sperm expenditure (i.e., used up more of their sperm reserves) than did low-risk males. A control experiment, in which test males were treated but did not participate in the mating trials, revealed no significant difference in the number of sperm stripped from high- and low-risk males, indicating that sperm production was not affected by the treatment. We did not detect a difference in the number of sperm retrieved from females among the groups, raising the possibility that some sperm are lost during mating activity, either through ejaculation with incomplete or interrupted penetration, or via female ejection. Copyright 2003.

A critical step for speciation in the face of gene flow is the origination of reproductive isolation. The evolution of assortative mating greatly facilitates this process. Assortative mating can be mediated by one or multiple cues across an array of sensory modalities. We here explore possible cues that may underlie female mate choice in a sympatric species pair of cichlid fish from Lake Victoria, Pundamilia pundamilia and Pundamilia nyererei. Previous studies identified species-specific female preferences for male coloration, but effects of other cues could not be ruled out. Therefore, we assessed female choice in a series of experiments in which we manipulated visual (color) and chemical cues. We show that the visibility of differences in nuptial hue (i.e., either blue or red) between males of the 2 species is necessary and sufficient for assortative mating by female mate choice. Such assortment mediated by a single cue may evolve relatively quickly, but could make reproductive isolation vulnerable to environmental changes. These findings confirm the important role of female mate choice for male nuptial hue in promoting the explosive speciation of African haplochromine cichlids.

Sexual selection drives the evolution of exaggerated male ornaments in many animal species. Female ornamentation is now acknowledged also to be common but is generally less well understood. One example is the recently documented red female throat coloration in some threespine stickleback (Gasterosteus aculeatus) populations. Although female sticklebacks often exhibit a preference for red male throat coloration, the possibility of sexual selection on female coloration has been little studied. Using sequential and simultaneous mate choice trials, we examined male mate preferences for female throat color, as well as pelvic spine color and standard length, using wild-captured threespine sticklebacks from the Little Campbell River, British Columbia. In a multivariate analysis, we found no evidence for a population-level mate preference in males, suggesting the absence of directional sexual selection on these traits arising from male mate choice. Significant variation was detected among males in their preference functions, but this appeared to arise from differences in their mean responsiveness across mating trials and not from variation in the strength (i.e., slope) of their preference, suggesting the absence of individual-level preferences as well. When presented with conspecific intruder males, male response decreased as intruder red throat coloration increased, suggesting that males can discriminate color and other aspects of phenotype in our experiment and that males may use these traits in intrasexual interactions. The results presented here are the first to explicitly address male preference for female throat color in threespine sticklebacks.

Examen du contenu stomacal de 243 D.i. provenant de deux localites de la Monterey Bay, Californie. La proie preferentielle est l'anemone de mer Corynactis californica. La difference de selectivite semble etre liee aux defenses contre la predation presentees par diverses anemones. On doit donc etre prudent lorsque l'on emploie les termes de «specialiste» ou de «proie preferentielle»