Although gene flow is an important determinant of evolutionary change, the role of ecological factors such as specialization in determining migration and gene flow has rarely been explored empirically. To examine the consequences of dispersal ability and habitat patchiness on gene flow, migration rates were compared in three cactophagous longhorn beetles using coalescent analyses of mtDNA sequences. Analyses of covariance were used to identify the roles of dispersal ability and habitat distribution in determining migration patterns. Dispersal ability was a highly significant predictor of gene flow (p < 0.001), and was more important than any other factor. These findings predict that dispersal ability may be an import factor shaping both microevolutionary and macroevolutionary patterns; this prediction is borne out by comparisons of species diversity in cactus-feeding groups.

Adaptive radiations consist of two intertwined processes, diversification of species and diversification of their ecological niches, but it is unclear whether there is a causal link between the processes. In phytophagous insects, ecological diversification mainly involves shifts in host-plant associations and in larval feeding habits (internal or external) on different plant parts, and several observations indicate that speciation is facilitated by host shifts. Data on host use in individual species suggest that internal feeders are less likely to colonize new hosts than external-feeding taxa and, consequently, increases in collective host ranges and species numbers should be slowed down in endophagous lineages. We tested these related hypotheses by using phylogenetic information to reconstruct the evolutionary history of larval resource use in the sawfly subfamily Nematinae, a group of 1000 plus species with a broad range of niches: the subfamily's combined host range includes over 20 plant families, and larvae may feed externally on leaves or needles, or internally, for example, in buds, fruits, leaves, or galls. The results show that: (1) Most internally feeding groups have evolved independently from external-feeding ancestors, but several distinct internal habits have appeared convergently multiple times; (2) Shifts among host taxa are clearly more common than changes in larval habits; (3) The majority of host switches have occurred among phylogenetic ally close plant groups, but many shifts are manifest among distantly related, ecologically proximate hosts; (4) Although external feeding characteristic of the common ancestor of Nematinae is associated with relatively high rates of host-shifting, internal feeders are very conservative in their host use; (5) In contrast, the effect of endophagy on speciation probabilities is more variable: net speciation rates are lowered in most internal-feeding groups, but a striking exception is found in species that induce galls on Salicaceae. The loose connection between collective host ranges and species diversity provides empirical support for theoretical models suggesting that speciation rates are a function of a complex interplay between "intrinsic" niche width and resource heterogeneity.

Nematinae is one of the largest subfamilies in the sawfly family Tenthredinidae, but internal relationships are unknown in the absence of any formal phylogenetic analysis. To understand the internal phylogeny of Nematinae, we sequenced a portion of the mitochondrial cytochrome oxidase I gene and the nuclear elongation factor-1 alpha gene from thirteen outgroup taxa and sixty-eight nematine species, the ingroup taxa of which represent all major genera and subgenera within the subfamily. Maximum parsimony and Bayesian phylogenetic analyses of the DNA sequence data show that: (1) Nematinae are monophyletic in a broad sense which includes Hoplocampa, Susana and the tribe Cladiini, which have been classified often into separate subfamilies; together with Craterocercus, these taxa form a paraphyletic basal grade with respect to the remaining Nematinae, but among-group relationships within the grade remain weakly resolved; (2) the remainder of the ingroup, Nematinae s. str, is monophyletic in all combined-data analyses; (3) within Nematinae s. str, the 'Higher' Nematinae is divided into three groups, Mesoneura and the large tribes Nematini and Pristiphorini; (4) although the traditional classifications at the tribal level are largely upheld, some of the largest tribes and genera are obviously para- or polyphyletic; (5) according to rate-smoothed phylogenies dated with two fossil calibration points, Nematinae originated 50-120 million years ago. In addition, the results from all Bayesian analyses provide strong and consistent support for the monophyly of Tenthredinidae, which has been difficult to demonstrate in previous parsimony analyses of morphological and molecular data.

A potential citrus pest, the Old World swallowtail butterfly Papilio demoleus L. was recently discovered in the Dominican Republic; however, there are many subspecies of this butterfly and not all are considered pests of citrus. We used genetic markers to determine the source population (subspecies), by comparing sequences from butterflies collected in the Dominican Republic with individuals whose provenance was known, and to indicate whether single or multiple introductions had taken place. Sequences of up to 1,400 nucleotides from the mitochondrial cytochrome oxidase subunit I gene were characterized from 28 specimens collected in the Dominican Republic and compared with known P. demoleus sequences available from GenBank. We confirmed earlier estimates, based on morphology, that the butterflies had originated in Southeast Asia, where the species is known to be a citrus pest. Lack of sequence variation among specimens from the Dominican Republic suggests that a single introduction in early 2004 was most likely. It is not known bow the butterflies reached the Dominican Republic.

Monodominant forests are a widespread feature of the humid and wet lowland tropics, but little is known about their origins or factors mediating their persistence. Nonetheless, escape from significant vertebrate and invertebrate seed predation plays a prominent role in most hypotheses. The seeds of Pentaclethra macroloba (Fabaceae: Mimosoideae) have long been thought to be virtually immune to predation, contributing to its local dominance in the canopy of some Mesoamerican forests. Here, we describe herbivory by the larvae of Carmenta surinamensis (Lepidoptera: Sesiidae) on the seeds of P. macroloba, and report the results of studies designed to clarify how this interaction influences germination, seedling growth, and mortality. To this end, we collected P. macroloba seeds at 30-d intervals for 5 mo along a rain forest transect in Costa Rica. The seeds were monitored in a shade house for 30 d. Adult moths were reared from 43.6 percent of seeds, and significantly affected germination and mortality, and all measures of growth (number of leaves, seedling height, seed and seedling mass at 30 d, and 30-d change in seed and seedling mass). Based on these observations, we conclude that seed boring by C. surinamensis is a potentially important factor influencing population dynamics in P. macroloba, and warrants further investigation for its prospective role in regulating local abundance in this locally dominant and ecologically significant tree.

The high extant species diversity of tropical lineages of organisms is usually portrayed as a relatively recent and rapid development or as a consequence of the gradual accumulation or preservation of species over time. These explanations have led to alternative views of tropical forests as evolutionary "cradles" or "museums" of diversity, depending on the organisms under study. However, biogeographic and fossil evidence implies that the evolutionary histories of diversification among tropical organisms may be expected to exhibit characteristics of both cradle and museum models. This possibility has not been explored in detail for any group of terrestrial tropical organisms. From an extensively sampled molecular phylogeny of herbivorous Neotropical leaf beetles in the genus Cephaloleia, we present evidence for (i) comparatively ancient Paleocene-Eocene adaptive radiation associated with global warming and Cenozoic maximum global temperatures, (it) moderately ancient lineage-specific diversification coincident with the Oligocene adaptive radiation of Cephaloleia host plants in the genus Heliconia, and (iii) relatively recent Miocene-Pliocene diversification coincident with the collision of the Panama arc with South America and subsequent bridging of the Isthmus of Panama. These results demonstrate that, for Cephaloleia and perhaps other lineages of organisms, tropical forests are at the same time both evolutionary cradles and museums of diversity.