No abstract

The valley of Cuatro Ciénegas in Mexico has the highest degree of local endemicity of any habitat in North America. A large number of endemic aquatic species occur both in the Cuatro Ciénegas basin and in the upper parts of the Río Salado de los Nadadores drainage, located immediately to the east of the valley. No natural surface flow occurs between these basins but artificial canals connect both areas. It is not clear whether the sharing of endemics between the Cuatro Ciénegas basin and the Río Salado is due to migration through canals. We conducted a phylogeographic study of mitochondrial haplotypes of the endemic shrimp Palaemonetes suttkusi to determine the evolutionary distinctiveness of the population found in Río Salado. We discovered that P. suttkusi likely has occurred naturally in both basins well into the distant past. Based on molecular clock analyses of the COI gene, the populations in the Río Salado and much of the Cuatro Ciénegas basin likely began diverging from each other between 1.9 and 11.2 Myr ago. The general levels of divergence are substantial but our results suggest there has also likely been recent gene flow between these basins. This is consistent with migration through human-made canals, but also consistent with the occurrence of natural gene flow during intermittent wet periods in the past million years. We also found significant differentiation of the Pozas Azules area from the rest of the Cuatro Ciénegas basin, a finding that is concordant with several phylogeographic studies on other aquatic endemics in Cuatro Ciénegas. We recommend that the upper parts of the Río Salado, the Pozas Azules area, and the rest of the Cuatro Ciénegas basin should each be considered independent evolutionarily significant units for conservation, and that migration of species through humanmade canals should be monitored and controlled.

The geographic mosaic theory of coevolution predicts 1) spatial variation in predatory structures as well as prey defensive traits, and 2) trait matching in some areas and trait mismatching in others mediated by gene flow. We examined gene flow and documented spatial variation in crushing resistance in the freshwater snails Mexipyrgus churinceanus, Mexithauma quadripaludium, Nymphophilus minckleyi, and its relationship to the relative frequency of the crushing morphotype in the trophically polymorphic fish Herichthys minckleyi. Crushing resistance and the frequency of the crushing morphotype did show spatial variation among 11 naturally replicated communities in the Cuatro Ciénegas valley in Mexico where these species are all endemic. The variation in crushing resistance among populations was not explained by geographic proximity or by genetic similarity in any species. We detected clear phylogeographic patterns and limited gene flow for the snails but not for the fish. Gene flow among snail populations in Cuatro Ciénegas could explain the mosaic of local divergence in shell strength and be preventing the fixation of the crushing morphotype in Herichthys minckleyi. Finally, consistent with trait matching across the mosaic, the frequency of the fish morphotype was negatively correlated with shell crushing resistance likely reflecting the relative disadvantage of the crushing morphotype in communities where the snails exhibit relatively high crushing resistance.

SummaryBare-necked Umbrellabird Cephalopterus glabricollis is endemic to Costa Rica and western Panama. It eats fruit, breeding at high elevations (> 800 m) and migrating to lower elevations during the non-breeding season. Using data from transect counts and radio-telemetry, we monitored bird movements in a protected area (Monteverde-ArenalSan Ramón reserves) in the Tilarán Mountains, Costa Rica. We also monitored fruit abundance along an altitudinal gradient to explore the potential relationship between bird movements and the abundance of the fruits this species consumed. The presence and abundance of umbrellabirds at high elevations (1,400 m) during the breeding season (March-June) coincided with the highest peak of fruit abundance. The presence of umbrellabirds in the lowlands (400 m) during the non-breeding season overlapped with the period of highest fruit abundance at these elevations. At middle elevations, bird presence and abundance did not correlate with fruit abundance. Radio-tagged birds left the protected area during the non-breeding season and there were no umbrellabirds inside the protected area during this period. Habitats where this species bred were well represented in the protected area but the habitat where they spent the non-breeding season was poorly represented, and was not adequately protected. This represents a potential threat to this species in the Tilarán Mountains.

The ocellated antbird (Phaenostictus mcleannani) feeds in groups and therefore is an informative species in which to study the biological factors that modulate avian group living. These birds congregate at swarms of army ants to capture fleeing prey, and previous observations suggest that males may be philopatric, feed with close relatives, and defend communal feeding ranges. We assessed whether kin selection could be an important factor maintaining group formation in a population of ocellated antbirds inhabiting continuous forest at La Selva Biological Station, Costa Rica, using radiotelemetry and 15 novel microsatellite markers. We predicted that the roosting areas of closely related adult males should overlap and that adult males feeding simultaneously at the same swarm should be highly related. We banded and genotyped 65 individuals (>or= 88% of the population) and radiotagged 30 of them. The results generally did not conform to our predictions. Little overlap occurred among the roosting areas of same-sex individuals, and nearest roosting neighbours (either same or opposite sex) were generally unrelated. A small proportion of male dyads suggested short-distance dispersal, but in general the distribution of genotypes within the study area approached randomness. We found little evidence of natal philopatry in either sex. Less than half of the feeding groups sampled included highly related males; most consisted of unrelated individuals. Hence, we found limited potential for kin selection to favour group living and suggest that other factors, particularly direct benefits (e.g. food intake), are probably more important than indirect effects (nepotism).