Michael J. Childress

Predation risk, gender and the group size effect: does elk vigilance depend upon the behaviour of conspecifics?

Many animals benefit from the presence of conspecifics by reducing their rate of scanning for predators while increasing their time spent foraging. This group size effect could arise from a decreased perception of individual risk (dilution hypothesis) and/or an increased ability to detect predators (detection hypothesis). We compared individual and group vigilance of Rocky Mountain elk, Cervus elaphus, in three regions of Yellowstone National Park, Wyoming, U.S.A. that varied in their encounter frequency with coyote, Canis latrans, grizzly bear, Ursus arctos, and grey wolf,Canis lupus , predators. Adult females without calves increased scanning and decreased foraging with high encounter risk and small herd size. Adult females with calves increased scanning and decreased foraging with high encounter risk, but showed no decrease in scanning with large herd size. Yearlings increased scanning and decreased feeding with small herd size, but not with high encounter risk. Adult males were least vigilant, fed most and were not influenced by encounter risk or herd size. These age–sex class differences led to significant differences in group vigilance depending on the composition of the herd. Herds with a majority of mothers were significantly more vigilant than herds with a majority of adult males. However, these differences in group vigilance had no influence on the individual scanning of females without calves. Thus, the decrease in individual scanning with herd size may depend more on changes in individual risk than on cooperative detection of predators. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Molecular phylogeny of the spiny lobster genus Panulirus (Decapoda: Palinuridae)

Phylogenetic relationships among all described species and four subspecies (total of 21 taxa) of the spiny lobster genus Panulirus White, 1847, were examined with nucleotide sequence data from portions of two mitochondrial genes, large-subunit ribosomal RNA (16S) and cytochrome oxidase subunit I (COI). Multiple sequence alignments were subjected to maximum-parsimony, neighbour-joining, and maximum-likelihood analysis with Jasus edwardsii as the outgroup. Two major lineages within Panulirus were recovered by all three methods for both the 16S and COI alignments analysed separately and for the combined alignment. The first lineage included all species of Panulirus classified as Groups I and II by previous morphologically based definitions. The second included all species classified as Groups III and IV. Relationships within major lineages were not well resolved; the molecular phylogeny did not support separation of Group I from Group II or of Group III from Group IV. The degree of sequence divergence between different pairs of species was higher in pairwise comparisons between species in Group I/II (16S: 2.8–19.4%; COI: 12.4–31.8%) than in those between species in Group III/IV (16S: 5.3–13.2%; COI: 12.6–19.6%). This pattern suggests that the Group I/II lineage may represent an earlier radiation of species within Panulirus.

Seasonal Prevalence of Hematodinium sp. Infections of Blue Crabs in Three South Carolina (USA) Rivers

Blue crab, Callinectes sapidus, commercial landings in the USA have been declining at an alarming rate. In South Carolina, these declines are significantly correlated with years of decreased rainfall and elevated salt marsh salinity. Previous studies suggest that higher salinity increases the risk of infection by Hematodinium sp., a dinoflagellate parasite of blue crabs, C. sapidus. A 4-year survey (June 2008 to March 2012) of blue crabs in the ACE Basin National Estuarine Research Reserve documented (1) the temporal and spatial patterns of Hematodinium sp. infection in relation to salinity, (2) some environmental correlates of disease prevalence, and (3) the characteristics of infected blue crabs. Sampling was conducted four times a year in March, June, September, and December in the South Edisto, Ashepoo, and Combahee rivers beginning in June 2008. Crab hemolymph samples were collected and preserved and DNA was successfully amplified for 2,303 individuals. Hematodinium sp. infection was evaluated by PCR amplification of its 18S rRNA gene and adjacent regions. Prevalence was highest in December 2008 in the Combahee River at sites closest to St. Helena Sound. The spatial and temporal pattern of Hematodinium sp. infection was correlated with several environmental parameters. Infected crabs exhibited differences in carapace shape and body condition compared to uninfected crabs. Overall, these results suggest that blue crabs in regions of higher salinity are at greater risk of infection by Hematodinium sp. and infected individuals exhibit sub-lethal effects of the disease.

Phylogenetic Evidence for the Gain and Loss of a Sexually Selected Trait in Sailfin Mollies

A phylogenetic comparative approach was used to examine the evolution of the enlarged “sailfin,” characteristic of the monophyletic lineage of sailfin mollies (Poecilia: Mollienesia), but absent in one of its species, P. latipunctata. Ancestral character state reconstructions demonstrated that the ancestral sailfin molly possessed the enlarged sailfin, and, thus, males of P. latipunctata have secondarily lost this trait. The strength of female mating preference was measured in P. latipunctata for two known targets of sexual selection, large male size, and sailfin male phenotype. Females of P. latipunctata preferred conspecific males of larger body size to those of smaller body size, but showed no preference for sailfin males of a related species, P. velifera, when compared with males of the shortfin species, P. mexicana. Taken together, these results suggest that the targets of sexual selection may have shifted in this species and that reduction in female preference for sailfin males may have played a role in the loss of this ornament.