RESUMO
BACKGROUND: Introduced predators at seabird colonies and parasites may have lethal and/or sub-lethal consequences for bird populations. We assessed the potential sub-lethal negative effects of these stressors in a native seabird listed as vulnerable in its south-eastern pacific distribution. This study was conducted in two red-tailed tropicbird (Phaethon rubricauda) colonies, one located in Rapa Nui Island, which is threatened by the presence of introduced predators, and the other located in Salas & Gómez Island, which has no introduced predators, but birds are infested by ectoparasitic louse flies. METHODS: The effects on physiological stress traits of both, predation risk on different nest types (protected and exposed) on Rapa Nui, and different levels of louse flies' parasitic loads on Salas & Gómez were studied. Three variables were analyzed: the heterophil/lymphocyte (H/L) ratio, the transcriptional levels of mRNA HSP70 in blood, and the body condition. These stress indicators and leukocyte counts were compared between colonies. RESULTS: No significant differences were found in any stress indicator between different nest types within Rapa Nui, showing that the effect of predator's presence was the same for adults nesting in both, protected and exposed nests. No significant correlation was found between louse flies' parasitic loads and any stress indicators in the birds of Salas & Gómez. Also, there was no difference in any stress indicator between islands. However, a significant opposite trend between islands was found in the eosinophil, lymphocyte, and monocyte counts when related to body condition. CONCLUSIONS: We found a lack of significant differentiation in all the stress level indicators assessed within and between islands. The presence of louse flies in Salas & Gómez vs. the absence of this parasite at Rapa Nui may be the cause for the significant difference in the trend of eosinophil, lymphocyte and monocyte counts between the islands. However, further studies are necessary to elucidate the reason for this difference and to better investigate the lethal effects of introduced predators on the Rapa Nui colony to evaluate appropriate conservation measures for this native seabird.
RESUMO
BACKGROUND: There is a biogeographic break located at 30°S in the southeast Pacific, in a coastal area of strong environmental discontinuities. Several marine benthic taxa with restricted dispersal have a coincident phylogeographic break at 30°S, indicating that genetic structure is moulded by life history traits that limit gene flow and thereby promote divergence and speciation. In order to evaluate intraspecific divergence at this biogeographic break, we investigated the genetic and morphological variation of the directly developing beach isopod Excirolana hirsuticauda along 1900 km of the southeast Pacific coast, across 30°S. RESULTS: The COI sequences and microsatellite data both identified a strong discontinuity between populations of E. hirsuticauda to the north and south of 30°S, and a second weaker phylogeographic break at approximately 35°S. The three genetic groups were evidenced by different past demographic and genetic diversity signatures, and were also clearly distinguished with microsatellite data clustering. The COI sequences established that the genetic divergence of E. hirsuticauda at 30°S started earlier than divergence at 35°. Additionally, the three groups have different past demographic signatures, with probable demographic expansion occurring earlier in the southern group (south of 35°S), associated with Pleistocene interglacial periods. Interestingly, body length, multivariate morphometric analyses, and the morphology of a fertilization-related morphological character in males, the appendix masculina, reinforced the three genetic groups detected with genetic data. CONCLUSIONS: The degree of divergence of COI sequences, microsatellite data, and morphology was concordant and showed two geographic areas in which divergence was promoted at differing historical periods. Variation in the appendix masculina of males has probably promoted reproductive isolation. This variation together with gene flow restrictions promoted by life history traits, small body size, oceanographic discontinuities and sandy-beach habitat continuity, likely influenced species divergence at 30°S in the southeast Pacific coast. The degree of genetic and morphological differentiation of populations to the north and south of 30°S suggests that E. hirsuticauda harbours intraspecific divergence consistent with reproductive isolation and an advanced stage of speciation. The speciation process within E. hirsuticauda has been shaped by both restrictions to gene flow and a prezygotic reproductive barrier.
