Biogeography: Marine Invaders of South America
The rivers of South American harbour a rich diversity of marine-derived lineages. These are taxa that are primarily distributed in oceans and seas, but include one or more species that are freshwater endemics. Marine derived fish lineages include stingrays, herrings, anchovies, toadfishes, needlefishes, drums, soles, and pufferfishes. Iniid dolphins, and several Neotropical freshwater invertebrate clades also appear to be marine derived.
Several hypotheses have been proposed to explain the origins of this unique component of the Neotropical aquatic fauna. These range from simple dispersal/invasion scenarios to explanations that invoke the role of specific paleogeographic events, such the orogeny of the Andes, the reversal of the Amazon, and marine incursions into the upper Amazon. Each hypothesis makes predictions concerning the timing of origin of marine-derived clades, and phylogenetic and biogeographic patterns shown by the marine and freshwater clades.
My investigations utilize phylogenetic trees and molecular age estimates from several marine-derived fish clades to test the hypotheses described above. To date, I have conducted analyses of stingrays (Lovejoy, 1996; Lovejoy, 1997, Lovejoy et al., 1998) and two different clades of needlefishes (Lovejoy and Collette, 2000). Patterns from these taxa are most compatible with origination of marine-derived lineages as a result of extensive marine incursions into the upper Amazon that occurred during the Miocene (Lovejoy, in press). Recently, I have begun collaborations with a Brazilian team of researchers to integrate molecular systematics, biogeography, and parasitology of freshwater drum (Sciaenidae) ( http://zoo.bio.ufpr.br/mono/ ). I am also beginning molecular systematic studies of anchovies (Engraulididae). Examination of multiple taxa is important, because congruence of phylogenetic and biogeographic patterns provides a powerful test of shared responses to the same paleogeographic event.
From a methodological perspective, I am interested in ways of calibrating and assessing the reliability of molecular clocks and estimates of age data. Marine-derived lineages present a special challenge because the transition from marine to freshwater habitats appears to be associated with an increased rate of molecular evolution. Another avenue of research is the comparison of physiological evolution in replicated pairs of marine/freshwater sister lineages. Synthesis of these approaches will illuminate several aspects of the origin and evolution of this unique component of freshwater biodiversity.
Potamorrhaphis guianensis from Peru
Plagiscion sp. (drum) from Venezuela
Anchoviella sp. from Peru
Colomesus sp. from Venezuela
Pellona , Belem Market, Iquitos, Peru