Gilbert Barrantes

Effect of urbanization on the avifauna in a tropical metropolitan area

The rapid and unplanned expansion of urban areas is a common pattern in neotropical developing countries. Urbanization has eliminated or drastically altered large areas of natural habitats used by the rich neotropical avifauna. In our study area, in Costa Rica’s Central Valley, urbanization increased 72% in 33 years with the consequent destruction, fragmentation, and isolation of forest tracts, shade plantations, and other semi-natural habitats used by a rich avifauna. We show that over the last 16 years 32 resident species of birds have disappeared from this area. Species with specialized habitat requirements or particular life history traits (e.g., altitudinal migrants) are disproportionately represented among those birds that have disappeared from the region. Another 34 latitudinal migrants have gone undetected as nearly all habitats these species used as a stopover site during the autumn migration have disappeared; many of these migrants were very abundant 16 years earlier. Relative abundance has also decreased for most resident and migratory species that remained or visited the area. If uncontrolled urban expansion continues, we predict that the rate of extinction of the avifauna that originally inhabited this region would continue possibly increasing.

The evolution of prey‐wrapping behaviour in spiders

We traced the evolution of silk use by spiders in attacks on prey by combining previous publications with new observations of 31 species in 16 families. Two new prey‐wrapping techniques are described. One, in which the spider holds a tense line (often covered with viscid silk) with both legs IV and applies it to the prey with a simultaneous movement of both legs, may be a synapomorphy linking Theridiidae, Nesticidae, and Synotaxidae. The other, in which the spider stands over the prey and turns in place, is apparently very ancient; it occurs in Theraphosidae, Tengellidae, and Agelenidae. The use of legs IV to wrap prey is described for the first time in Filistatidae and Scytodidae. Using a recent phylogeny of spiders, we propose that prey wrapping with legs IV has evolved convergently at least four times. We propose that prey wrapping originally evolved from egg‐sac construction behaviour.

Vestiges of an orb-weaving ancestor? The "biogenetic law" and ontogenetic changes in the webs and building behavior of the black widow spider Latrodectus geometricus (Araneae Theridiidae)

Young juveniles of L. geometricus fit the strong trend for “ontogeny to repeat phylogeny” previously documented in other web-building spiders; younger spiders were less likely to build the derived silk retreats that occur at the edges of webs of adults. Younger individuals also consistently built more highly organized webs, with radial lines that converge on a central, horizontal disc and that support regularly spaced, sticky “gumfoot“ lines. Some details of how radial and gumfoot lines were built suggest that the radial and gumfoot lines and the behavior involved in their construction may be homologous with traits associated with radii and sticky spirals in aranoid orb webs. The numerous convergences between the webs and building behavior of young L. geometricus and the highly modified webs and building behavior of genera of the orb weaving families Theridiosomatidae (Wendilgarda) and Anapidae (Comaroma), which have independently replaced orbs with webs designed to capture prey on surfaces near the web, suggest a new hypothesis for how gumfoot theridiid webs may have evolved from orbs.

Sexual behavior, cannibalism, and mating plugs as sticky traps in the orb weaver spider Leucauge argyra (Tetragnathidae)

Unpublished field observations in Leucauge argyra, a tropical orb weaver spider, suggest the occurrence of conspicuous mating plugs that could reduce or prevent remating attempts. Otherwise, the sexual behavior of this species remains unknown. The aims of this study were to describe the courtship behavior and copulation in L. argyra and investigate mating plug formation in this species. Fourteen virgin females and 12 plugged females were exposed to up to three males and checked for mating plug formation. Of the 12 virgins that copulated, nine produced plugs (five immediately after copulation), and the five plugged females that copulated produced another mating plug immediately after copulation. We did not detect the transfer of any male substance during copulation but observed a whitish liquid emerging from female genital ducts. Plug formation was positively associated with male twanging during courtship. One virgin and four plugged females cannibalized males. In seven trials with virgins and in three trials with plugged females, the male’s palp adhered to a substance that emerged from female genital ducts and spread on her genital plate. The male had to struggle energetically to free his glued palp; two of these males were cannibalized while trying to release their palps. Females seem to determine copulation duration by altering the timing of mating plug formation and through sexual cannibalism. This is the first case reported of a mating plug as a sticky trap for males.

RELATIONSHIP BETWEEN SPECIES RICHNESS OF EXCAVATOR BIRDS AND CAVITY-ADOPTERS IN SEVEN TROPICAL FORESTS IN COSTA RICA

Abstract The abundance of wood cavities is thought to be a limiting factor for bird species that depend on these cavities for nesting. Thus, it is expected that number of cavity adopters correlates with number of cavity excavators across communities. We used available published data to compare composition and richness of cavity adopters and cavity excavators across seven forest localities in Costa Rica. Species richness and composition of cavity excavator and cavity adopter bird assemblages varied among the seven forests. Species composition of excavators and adopters was more similar between nearby localities and between localities with similar forest types. Richness of wood-cavity adopters (using mostly cavities created by excavators) tended to increase with richness of excavators. The lack of association between cavity adopters and cavity excavators in some localities may be compensated by high abundance of a few species of excavators. The abundance of adopters and their dependence on forested habitats and on cavities excavated by woodpeckers varied largely across localities.

Courtship behavior and copulation in Tengella radiata (Araneae, Tengellidae)

Abstract The first description of the courtship behavior and copulation is provided for Tengella radiata (Kulczynski 1909). The male courts the female by rocking his body and vibrating his abdomen. These behaviors seem to induce the female to move out from her retreat onto the sheet and incline her body to facilitate intromission. The female has an active role during the courtship: strumming the tunnel and sheet threads, apparently inducing the male to increase the frequency and intensity of his courtship. Palpal insertion is extremely short. The female terminates the copulation by lunging at the male.

Repertoire Size and Syllable Sharing in the Song of the Clay-Colored Thrush (Turdus grayi)

Abstract Song repertoire size and extent of song sharing provide information about social interactions that occur in songbird species. We recorded the songs of eight male Clay-colored Thrushes (Turdus grayi) in San José, Costa Rica during the 2008 breeding season. We classified 695 songs and 5,032 syllables using visual inspection of spectrograms and spectrogram correlation analysis to measure repertoire size and syllable sharing among a local group of males. Male repertoire size was 10–17 syllable types. Males shared on average 28 ± 15% (SD) syllable types from their repertoires with other males, but a larger proportion of syllable types remained unique to particular males. Extent of repertoire sharing and distance between singing males were not related. Presence of shared and individually unique syllables in the repertoires indicate that imitation, and perhaps improvisation, contribute to development of the song of Clay-colored Thrushes.

Notes on the biology of Anelosimus pacificus Levi, 1963 (Theridiidae, Araneae)—evidence for an evolutionary reversal to a less social state

All hitherto studied Anelosimus species are social, either temporarily (subsocial) or permanently (quasisocial); the genus represents the largest known clade of social spiders. We provide behavioural data on Anelosimus pacificus Levi, 1956 (Theridiidae, Araneae) a species that hitherto was known from only a few specimens collected half a century ago. Anelosimus pacificus, unlike its better known congeners, is solitary for the majority of its lifespan with the juveniles passively receiving maternal care before dispersal at an early instar. Given the phylogenetic position of A. pacificus, this is an example of a behavioural reversal to a less social (solitary) state, and the first such reversal documented in spiders. Interestingly, linked with this is a reversal in other traits. Anelosimus pacificus web architecture, use of sticky silk, the ability of juveniles to emerge from the egg sac, and build and maintain webs without help from the mother, all more resemble traits in typical solitary theridiids than those in its social congeners. These observations may help elucidate what factors contribute to the evolution of sociality in spiders.

Static allometry and sexual size dimorphism in Centruroides margaritatus (Scorpiones: Buthidae)

Abstract Animal body traits are scaled relative to overall body size depending on the evolutionary context. Most naturally selected traits are scaled approximately isometrically (constitute a constant proportion of the body size at different body sizes), whereas those under sexual selection tend to present positive static allometry (be proportionally larger in larger individuals). However, there are body traits that might be influenced by both natural and sexual selection. We studied the courtship behavior of the scorpion Centruroides margaritatus (Gervais 1841) and analyzed the static allometry of several body traits. We hypothesized that those traits that were actively used in courtship and seemed to be sexually dimorphic could be under sexual selection. The main sexually dimorphic traits were body size (female larger) and metasoma length (male longer). Although metasoma length of males had a steeper allometric slope (larger males had longer metasoma) than that of females, the slopes did not differ significantly. All body traits measured showed isometry with body size, except that the pecten presented negative allometry in males. Thus the length of the metasoma of males, thought to be influenced by sexual rather than natural selection, did not present positive allometry as expected. Males used the metasoma actively while courting females.

Post-copulatory Sexual Selection in Two Tropical Orb-weaving Leucauge Spiders

This chapter focuses on descriptive and experimental studies of the sexual biology of two spider species, Leucauge mariana and Leucauge argyra . We examine general questions related to female effects on paternity by taking advantage of several unusual traits: direct female participation in forming copulatory plugs and physical clasping by the female rather than the male during copulation in both species; and derived traits in the genitalia of males and females and occasional female cannibalism of conspecific males by trapping the male’s genitalia in adhesive copulatory plugs in L. argyra. These derived traits, combined with other aspects of sexual interactions that are typical of spiders in general, such as complete, easy female avoidance of unwanted sexual advances of males, copulatory courtship by males, and imperfect male ability to remove copulatory plugs from the female’s genitalia, constitute a rich mixture from which clear lessons can be drawn. Post-copulatory sexual selection probably acts on male genitalia and their behavior in both species. Two derived male genitalic clasping and clamping devices L. argyra may be associated with the extremely aggressive female behavior. One genital structure in male L. mariana may have evolved under sexual selection by sperm competition to remove copulatory plugs from female genitalia . In contrast to expectations from theory based on male–female conflict, the female genitalia of L. argyra has a derived trait that selectively facilitates rather than impedes male genital clamping. In contrast to lock-and-key expectations, another prominent, derived female genital structure in L. argyra does not mesh with any male structure during copulation; it may instead function in sensing male genital movements . Additional non-genital male traits associated with copulation are also probably under post-copulatory sexual selection in both species. Experimental manipulations of male chelicerae and of possible female receptors of stimuli from the male chelicerae demonstrated that stimulation from secondary sexual modifications of the male chelicerae influences several female reproductive processes in L. mariana , including receptivity to remating , female interruption of copulation, and copulatory plug formation. Additionally, two male copulatory courtship behavioral patterns correlate with greater plug formation in L. mariana, and one pre-copulatory courtship behavioral pattern in males of L. argyra correlates with plug formation, suggesting additional possible male effects on post-copulatory female reproductive processes. Other male sexual behavior correlates with the timing of female emission of plug material that may affect a male’s chances of surviving the encounter. In sum, female Leucauge have powerful effects on whether copulation occurs, when it will end, whether a mating plug will be formed, and whether the male will survive the encounter. Several genital and non-genital male traits likely evolved under a mix of post-copulatory sexual selection (sperm competition and probably cryptic female choice [CFC]) to elicit favorable modulation of these female effects.