Factors affecting parasite prevalence among wild bumblebees

1. Bumblebees are important pollinators in North America and are attacked by a range of parasites that impact their fitness; however, few studies have investigated the extent or causes of parasitism in North America. 2. This study used a 2‐year multi‐site survey of bumblebee parasitism to ask: (i) how common are parasitoid conopid flies and the internal parasites Crithidia bombi and Nosema bombi in Massachusetts; and (ii) what factors are correlated with parasitism? 3. Infection rates by all three parasites were higher in this study than previously documented in North America. Overall, conopids infected 0–73% of bees in each sample, C. bombi infected 0–82% of bees, and N. bombi infected 0–32%. 4. Conopid flies infected female bees more than males and intermediate‐sized bees more than large or small bees. Crithidia bombi infection rates were higher in certain bee species and sites, and exhibited a unimodal pattern of prevalence over time. Nosema bombi parasitism was higher in male than female bees. 5. Infection by N. bombi in two rare bumblebee species was higher than expected based on parasitism rates of common bee species but C. bombi infection was lower. If high prevalence of N. bombi in these bumblebee species is common, parasitism may be a potential cause of their decline. 6. Given the documented effects of these parasites, the high levels of infection may affect bee populations in Massachusetts and threaten the stability of their valuable ecosystem services.     

Molecular systematics of Selenops spiders (Araneae: Selenopidae) from North and Central America: implications for Caribbean biogeography

The Caribbean region includes a geologically complex mix of islands, which have served as a backdrop for some significant studies of biogeography, mostly with vertebrates. Here, we use the tropical/subtropical spider genus Selenops (Selenopidae) to obtain a finer resolution of the role of geology in shaping patterns of species diversity. We obtained a broad geographic sample from over 200 localities from both the islands and American mainland. DNA sequence data were generated for three mitochondrial genes and one nuclear gene for eleven outgroup taxa and nearly 60 selenopid species. Phylogenetic analysis of the data revealed several biogeographic patterns common to other lineages that have diversified in the region, the most significant being: (1) a distinct biogeographic break between Northern and Southern Lesser Antilles, although with a slight shift in the location of the disjunction; (2) diversification within the islands of Jamaica and Hispaniola; (3) higher diversity of species in the Greater Antilles relative to the Lesser Antilles. However, a strikingly unique pattern in Caribbean Selenops is that Cuban species are not basal in the Caribbean clade. Analyses to test competing hypotheses of vicariance and dispersal support colonization through GAARlandia, an Eocene–Oligocene land span extending from South America to the Greater Antilles, rather than over‐water dispersal. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 288–322.     

A developing paradigm for the development of bird beaks

Some adaptive radiations are notable for extreme interspecific diversification in one or a few adult traits. How and why have trait differences evolved? Natural and sexual selection often provide answers to the question of why. An answer to the question of how is to be found in the genetic control of the phenotypic traits, especially in the early stages of development, when interspecific differences first become expressed. Recent studies of the molecular genetic control of beak development in Darwin's finches have shown that a signalling molecule (BMP4) plays a key role in the development of large and deep beaks. Expression of this molecule occurs earlier (heterochrony) and at higher levels in species with deep beaks compared with species with more pointed beaks. The implication of this finding is that variation in the regulation of one or a few genes that are expressed early could be the source of evolutionarily significant variation that is subject to natural selection in speciation and adaptive radiation. This view is reinforced by parallel findings with the same signalling molecule in the development of jaw morphology in cichlid fish of the Great Lakes of Africa. Further research into regulatory mechanisms is to be expected, as well as extension to other examples of radiation such as honeycreepers in Hawaii and Anolis lizards in the Caribbean. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88 , 17–22.     

The effect of suspended sediments on Lake Texoma Daphnia: field distributions and in situ incubations

1. We measured the abundance and eggs per female of four Daphnia species in turbid and relatively clear regions of Lake Texoma (Oklahoma‐Texas, U.S.A.) on 12 dates over the course of 5 years. 2. Two species, Daphnia lumholtzi and Daphnia parvula, occurred and reproduced in turbid locations, but two other species, Daphnia mendotae and Daphnia pulicaria, occurred almost exclusively in relatively clear conditions. 3. To test the hypothesis that interference with foraging excludes clear‐water Daphnia species from turbid locations, we incubated adult D. mendotae at both a clear and a turbid site. In three successive experiments D. mendotae individuals incubated at the turbid site carried as many or more eggs than individuals incubated at the clear site.     

Simulating secondary contact in allopatric speciation: an empirical test of premating isolation

Allopatric populations of Geospiza difficilis, the Sharp‐beaked Ground Finch, differ morphologically in association with different habitats to an extent unrivalled by any other species of Darwin's finch. The question arises as to whether they have diverged so much that they would not interbreed if they became sympatric; in other words, have they become separate species while remaining allopatric? In other species of Darwin's finches, it is known that a sexual imprinting‐like process based on early learning of song constrains breeding to conspecifics in sympatry. Therefore we used song playback experiments on Isla Genovesa to test the potential of G. difficilis to respond to songs from two other populations of the species on other, ecologically similar, islands. We found strong responses by males to songs of their own population, and heterogeneous but overall weaker responses to the structurally similar songs of G. difficilis from Isla Darwin. Tested birds did not respond to G. difficilis songs from Isla Wolf, songs of G. fuliginosa from Isla Pinta and control Cassin's finch songs. Female responses were infrequent and weak, apparently inhibited by the presence of responding males in most instances. Thus, assuming that females exercise similar discriminations to those of males, the Genovesa population of G. difficilis appears to be well advanced along the path of speciation: reproductively isolated from the Wolf population by a premating barrier to gene exchange that is culturally inherited, but not reproductively isolated from the Darwin population. We discuss the implications of imprinting for the process of speciation, the reasons for divergence of songs in allopatry, and the outcome of a hypothetical secondary contact in terms of coexistence, competition and interbreeding. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 76 , 545–556.     

Dynamics of Cell Redifferentiation in Dictyostelium mucoroides

During migration of a D. mucoroides slug, prespore cells at the immediate edge of the prespore-prestalk junction advance into the prestalk region in approximately 1.5 min. Redifferentiation of the prespore into prestalk cells occurs during this period. Evidence that the cells redifferentiated required autoradiographic, electron microscopic, and staining techniques. These methods determined that glycoprotein synthesis declined; prespore vesicles, the organelles found specifically in prespore cells, were degraded; and staining was reduced during this developmental transition into prestalk cells.