Soils from the Galapagos Islands

Morphologic Differentiation of the Exotic Parasitoid Eupelmus pulchriceps (Hymenoptera: Eupelmidae) in the Galapagos Archipelago

The historical and geographical properties of the archipelagos allow a detailed study of species diversification, and phenotypic traits can indicate the extent of such processes. Eupelmus pulchriceps (Cameron, 1904) is an exotic species to the Galapagos archipelago, and generalist parasitoid that attacks a beetle species that consumes the seeds of the invasive shrub Leucaena leucocephala (Lam.) de Wit. Despite extensive sampling, the wasp is recorded only in Santa Cruz and San Cristobal islands of the Galapagos archipelago. Thus, using 112 female wasps, we compare body size, proportion, and allometric differentiations within and between the two islands. There were no body size differences between islands. A PerMANOVA indicates differences between the islands and a single differentiation between two localities of one island. Allometric differences between islands were not the same for all structures. These results are consistent with the greater distance between islands than between localities and suggest a differentiation process. The variables with allometric differentiation are associated with wings and ovipositor, possibly responding to different ecological pressures. It is interesting that this parasitoid, recently arrived at the archipelago, is already showing differentiation. Also, it is essential to monitor the behavior of these wasps in the archipelago, given their potential to access other species affecting the trophic interactions of the local biota.

Cadmium retention and microbial response in volcanic soils along gradients of soil age and climate on the Galápagos Islands

The behavior of trace metals may vary strongly in the course of volcanic soil development. Cadmium retention in soils is specifically important for some Galápagos islands where agriculture is leading to anthropogenic Cd contamination. To assess the influence of soil development factors on soil Cd retention and toxicity, we performed Cd sorption-desorption experiments with volcanic topsoils from the Galápagos Islands sampled along gradients of (a) substrate age (chronosequence, 1.5-1,070 ka) and (b) climate (elevation sequence, 47-866 m asl) ranging from arid lowland areas to humid highland areas. Additionally, the effects of Cd toxicity on the soil microbial community composition were evaluated for two soils of the chronosequence. In young volcanic soils, the sorption capacity was very high but decreased rapidly with soil age and increasing elevation. These trends were coupled with decreases in soil weathering indicators (e.g., electrical conductivity, pH, and effective cation exchange capacity) as well as changes in soil mineralogy. Cadmium addition did not influence total phospholipid fatty acids and basal respiration in most soils. However, with increasing Cd concentration, a pronounced reduction in the Gram-negative/Gram-positive bacteria ratio (from 0.32 to 0.12) occurred in an old, highly weathered soil with low Cd retention capacity. Our results show that up to 60% of added Cd was only weakly sorbed in old volcanic soils. As a consequence, the old volcanic soils of Galápagos bear the potential risk that the mobile Cd fraction is taken up by soil microorganisms, transferring this element into the food chain.