A. Stanley Rand

Competition in Tropical Stream Fishes: Support for the Competitive Exclusion Principle

Two collections of fish were made from the same Panama lowland stream, one during the dry season, and a second during the wet season. Food overlaps among nine sympatric fish species were calculated for each collection by examining fish stomach contents. Species habitats and feeding methods were determined from field and laboratory observations. Estimates of food abundance, measured independently from food overlap, were made by direct and indirect methods, and were used to determine relative levels of competition. The results show that food overlaps among the fishes are at a minimum during the dry season. Food abundance is also lowest during the dry season, which suggests increased competition for food at this time. This seasonal coincidence of the most distinct species separations with the time of increased competition are exactly those consequences predicted by the principle of competitive exclusion. It is concluded that this study provides strong support for the validity of this principle.

Species recognition and sexual selection as a unitary problem in animal communication

We investigated patterns of mating call preference and mating call recognition by examining phonotaxis of female túngara frogs, Physalaemus pustulosus, in response to conspecific and heterospecific calls. There are four results: females always prefer conspecific calls; most heterospecific calls do not elicit phonotaxis; some heterospecific calls do elicit phonotaxis and thus are effective mate recognition signals; and females prefer conspecific calls to which a component of a heterospecific call has been added to a normal conspecific call. We use these data to illustrate how concepts of species recognition and sexual selection can be understood in a unitary framework by comparing the distribution of signal traits to female preference functions.

The sensory basis of sexual selection for complex calls in the túngara frog, Physalaemus pustulosus (sexual selection for sensory exploitation)

Male túngara frogs (Physalaemus pustulosus) vocalize to attract females, and enhance the attractiveness of their simple, whine‐only call by adding chucks to produce complex calls. Complex calls contain more total energy and are of longer duration. By virtue of the greater frequency range of the chuck, complex calls also simultaneously stimulate both the amphibian papilla and the basilar papilla of the frogs inner ear. Female phonotaxis experiments using synthetic stimuli demonstrate that an increase in the calls acoustic energy is not sufficient to account for the enhanced attractiveness of the complex call. However, the stimulation of either or both of the females sound‐sensitive inner‐ear organs is sufficient to elicit her preference. We suggest that the females sensory system generates selection that equally favors at least three evolutionary alternatives for enhancing call attractiveness and that historical constraints imposed by the males morphology determined which of the alternatives was more likely to evolve. These data are consistent with our hypothesis of sensory exploitation, which states that selection favors those traits that elicit greater stimulation from the females sensory system and which emphasizes the nonadaptive nature of female preference.

Ecological Distribution in Anoline Lizards of Puerto Rico

The eight species of lizards of the genus Anolis in Puerto Rico can be divided into four morphological similarities. One, Anolis curvieri, is very different from the rest and has not been discussed here. The other seven species fall into three groups. Each of these groups occupies a different structural habitat which can be defined in terms of perch height and perch diameter. Within each of these three groups the species have very similar but not indential structural habitats but differ very widely in climatic habitat defined in terms of shade. Shade preferences seem to result from the temperature preferences of the species involved. In each group there is one species with high shade preference which is essentially restricted to the mountains. Each group also has a species with a lower shade preference which occurs in the lowlands and extends up into the mountains in exposed or sunny situations. One of the three groups has an additional species which is restricted to the hot and southwest corner of Puerto Rico. When one compares the temperature preferences or eccritic temperatures of the various species, one finds in each group that the highland species has a lower eccritic temperature than does the lowland species. There is little temperature difference between the lowland species and arid southwest species in the group where this additional third species is present. The species within each structural habitat show many morphological similarities which may be the result of their being closely related or may be the result of adaptation to similar environments. The differences in microhabitat between the Puerto Rican anoles separate them spatially though not completely. In species occupying different structural habitats in the same area the overlap may involve part of the home range of most of the individuals in the area. In species occupying the same structural but different climatic habitats the overlap may involve all of the home range of some individuals but of only a small fraction of the individuals in the total population. The spatial separation among Puerto Rican Anolis can be suggested to be of ecological significance because it reduces interspecific competition and because it allows the various species to adapt more precisely to different parts of the available habitat. Thus members of a genus may exploit the habitat more efficiently.

Inverse Relationship Between Temperature and Shyness in the Lizard Anolis Lineatopus

An increase in flight distance with a decrease in body temperature in 32 male Anolis lineatopus at Mona, Jamaica, supports more casual field observations that these lizards are shier when they are cold than when they are warm. It is suggested that this increased shyness compensates for the slowing effects of lower temperatures on biological processes and so helps protect these arboreal lizards from warm—blooded predators. See full-text article at JSTOR

Fine-scale genetic pattern and evidence for sex-biased dispersal in the túngara frog, Physalaemus pustulosus

Túngara frogs (Physalaemus pustulosus) are a model system for sexual selection and communication. Population dynamics and gene flow are of major interest in this species because they influence speciation processes and microevolution, and could consequently provide a deeper understanding of the evolutionary processes involved in mate recognition. Although earlier studies have documented genetic variation across the species’ range, attempts to investigate dispersal on a local level have been limited to mark–recapture studies. These behavioural studies indicated high mobility at a scale of several hundred metres. In this study we used seven highly polymorphic microsatellite loci to investigate fine‐scaled genetic variation in the túngara frog. We analysed the influence of geographical distance on observed genetic patterns, examined the influence of a river on gene flow, and tested for sex‐biased dispersal. Data for 668 individuals from 17 populations ranging in distance from 0.26 to 11.8 km revealed significant levels of genetic differentiation among populations. Genetic differentiation was significantly correlated with geographic distance. A river acted as an efficient barrier to gene flow. Several tests of sex‐biased dispersal were conducted. Most of them showed no difference between the sexes, but variance of Assignment Indices exhibited a statistically significant male bias in dispersal.

Phylogeny of Frogs of the Physalaemus Pustulosus Species Group, With an Examination of Data Incongruence

Characters derived from advertisement calls, morphology, allozymes, and the sequences of the small subunit of the mitochondrial ribosomal gene (12S) and the cytochrome oxidase I (COI) mitochondrial gene were used to estimate the phylogeny of frogs of the Physalaemus pustulosus group (Leptodactylidae). The combinability of these data partitions was assessed in several ways: measures of phylogenetic signal, character support for trees, congruence of tree topologies, compatibility of data partitions with suboptimal trees, and homogeneity of data partitions. Combined parsimony analysis of all data equally weighted yielded the same tree as the 12S partition analyzed under parsimony and maximum likelihood. The COI, allozyme, and morphology partitions were generally congruent and compatible with the tree derived from combined data. The call data were significantly different from all other partitions, whether considered in terms of tree topology alone, partition homogeneity, or compatibility of data with trees derived from other partitions. The lack of effect of the call data on the topology of the combined tree is probably due to the small number of call characters. The general incongruence of the call data with other data partitions is consistent with the idea that the advertisement calls of this group of frogs are under strong sexual selection.

Allozyme and advertisement call variation in the tungara frog, Physalaemus pustulosus

We analyzed variation in advertisement calls and allozymes in 30 populations along a 5000‐km transect throughout most of the range of the túngara frog, Physalaemus pustulosus. All 12 call variables measured show significant differences among populations despite the importance of the advertisement call in species recognition. Some call variables exhibited clinal variation, whereas most others differed between the two major allozyme groups that have invaded Panama at different times, perhaps 4–4.5 million yr apart. Call variables that primarily affect discrimination among conspecifics tended to exhibit greater variation than call variables that are crucial for species recognition. The proximate mechanism of production underlying a call variable, however, is a better predictor of its variation. Contrary to predictions of some sexual selection models, call variation exhibits predictable patterns of geographical variation, although a substantial portion of variation among populations is not explained by geographic position. Although allozymes, calls, and geography usually covary, closer populations can have more similar calls independent of allozyme similarity.

The vocal sac as a visual cue in anuran communication: an experimental analysis using video playback

Acoustic signals produced by most anurans are accompanied by inflation of a conspicuous vocal sac. We presented female tungara frogs, Physalaemus pustulosus, with acoustic playback of the male advertisement call, synchronized with a video playback of vocal sac inflation. Females significantly preferred a stimulus combination including vocal sac inflation over an identical set of stimuli with the vocal sac inflation removed. Neither a moving rectangle bearing the gross contrast and spatiotemporal properties of the vocal sac inflation sequence, nor the image of a noncalling male significantly enhanced the attractiveness of the acoustic stimulus. Both the form and spatiotemporal properties of the vocal sac thus appear to be salient to females. The results indicate that the vocal sac can serve as a visual cue, which may account for the conspicuous pigmentation found on the vocal sacs of males in many species. Gular inflation in synchrony with a call may function to facilitate female localization of individual males in an aggregation.

Dietary source for skin alkaloids of poison frogs (Dendrobatidae)

A wide range of alkaloids, many of which are unknown elsewhere in nature, occur in skin of frogs. Major classes of such alkaloids in dendrobatid frogs are the batrachotoxins, pumiliotoxins, histrionicotoxins, gephyrotoxins, and decahydroquinolines. Such alkaloids are absent in skin of frogs (Dendrobates auratus) raised in Panama on wingless fruit flies in indoor terraria. Raised on leaf-litter arthropods that were collected in a mainland site, such terraria-raised frogs contain tricyclic alkaloids including the beetle alkaloid precoccinelline, 1,4-disubstituted quinolizidines, pyrrolizidine oximes, the millipede alkaloid nitropolyzonamine, a decahydroquinoline, a gephyrotoxin, and histrionicotoxins. The profiles of these alkaloids in the captive-raised frogs are closer to the mainland population ofDendrobates auratus at the leaf-litter site than to the parent population ofDendrobates auratus from a nearby island site. Extracts of a seven-month sampling of leaf-litter insects contained precoccinelline, pyrrolizidine oxime236 (major), and nitropolyzonamine (238). The results indicate a dietary origin for at least some “dendrobatid alkaloids,” in particular the pyrrolizidine oximes, the tricyclic coccinellines, and perhaps the histrionicotoxins and gephyrotoxins.