Are Infaunal Predators Important in Structuring Marine Soft-Bottom Communities?

The role of infaunal predators in structuring marine soft-bottomcommunities was evaluated according to these predators': 1)effects on prey density based on manipulative field experiments,2) feeding rates, 3) effects on prey distribution, 4) effectson species diversity, and 5) interactions with their prey. Estimatesof feeding rates indicate that many predatory taxa have thepotential to reduce the size of prey populations and suggestthat nemerteans are likely to have a larger impact on infaunalabundances than polychaetes. Infaunal predators have been demonstratedto have a significant effect on infaunal densities and to affectthe spatial and temporal distribution of their prey. The effectsof these predators on species diversity apparently depend onthe predator and the diversity of the system. These conclusionsmay not be applicable to all soft-bottom habitats or all groupsof infaunal predators because they are based on studies of veryfew taxa conducted almost exclusively in intertidal, unvegetated,mud habitats. Additional studies are needed on the effects ofpredation by infauna on infaunal population dynamics and onthe mechanisms of interactions between predator and prey. Furtherinvestigation will probably reveal that different groups ofinfaunal predators play different roles in structuring soft-bottomcommunities.     

A splice site variant in the SUV39H2 gene in Greyhounds with nasal parakeratosis

Hereditary nasal parakeratosis (HNPK), described in the Labrador Retriever breed, is a monogenic autosomal recessive disorder that causes crusts and fissures on the nasal planum of otherwise healthy dogs. Our group previously showed that this genodermatosis may be caused by a missense variant located in the SUV39H2 gene encoding a histone 3 lysine 9 methyltransferase, a chromatin modifying enzyme with a potential role in keratinocyte differentiation. In the present study, we investigated a litter of Greyhounds in which six out of eight puppies were affected with parakeratotic lesions restricted to the nasal planum. Clinically and histologically, the lesions were comparable to HNPK in Labrador Retrievers. Whole genome sequencing of one affected Greyhound revealed a 4‐bp deletion at the 5′‐end of intron 4 of the SUV39H2 gene that was absent in 188 control dog and three wolf genomes. The variant was predicted to disrupt the 5′‐splice site with subsequent loss of SUV39H2 function. The six affected puppies were homozygous for the variant, whereas the two non‐affected littermates were heterozygous. Genotyping of a larger cohort of Greyhounds revealed that the variant is segregating in the breed and that this breed might benefit from genetic testing to avoid carrier × carrier matings.     

The variation in frequency with which markers are transduced by phage P1 is primarily a result of discrimination during recombination

Summary The efficiency of recovery of P1 transductants is marker dependent and normally varies over a 25-fold range. UV irradiation of either transducing lysates or recipient cells results in a selective stimulation of the transduction of markers which are normally transduced poorly. As a result the range in frequency of transduction is reduced to about 3-fold and resembles the gene frequency distribution expected in the donor cells. We conclude that P1 transducing lysates are likely to contain a random sample of donor DNA but that the recombination system of the recipient cell exhibits a preference for the DNA of some regions over that of others. Damage to DNA presumably overrides this specificity.     

Testing for MacArthur-Wilson Equilibrium with the Arthropods of the Miniature Spartina Archipelago at Oyster Bay, Florida

SYNOPSIS. The unique features of the MacArthur-Wilson modelof equilibrium biogeography are the immigration and extinctioncurves. In the model, the immigration rate for each island isnegatively correlated with species number, and island extinctionrate is positively correlated with species number. Direct tests of the sign and statistical significance of immigrationand extinction curves were done, with data on arthropods oftiny Spartina alterniflora islets, in north Florida. Rey (1981)defaunated six islets in the spring, then censused the recolonizationweekly, for one year. Two control islets and a mainland plotwere also censused. Distinct tendencies in favor of MacArthur-Wilsoncorrelations were present for both immigration and extinction.But sufficient extraneous variation occurs in immigration andextinction rates to make correspondence to MacArthur-Wilsoncurves statistically non-significant, unless probabilities arecombined among islands. Thus, mathematical deductions from theMacArthur-Wilson model, which treat the curves as deterministiclines with no variance, are less appropriate than approachesthat incorporate stochastic variation. The study of community patterns, by models such as the MacArthur-Wilsonmodel, are not a substitute for careful autecological studies.Mechanisms of colonization and co-existence are only dimly hintedat by gross community patterns.