Sex determination in crayfish: are intersex Cherax quadricarinatus (Decapoda, Parastacidae) genetically females?

In the Australian red-claw crayfish Cherax quadricarinatus (von Martens) (Decapoda, Parastacidae), a gonochoristic species, seven different combinations of intersex individuals (with both male and female genital openings) have been described. However, to date, the genetic basis for this phenomenon has not been investigated. This study was designed to test a simple chromosome-based sex-determination model for C. quadricarinatus that assumes the male to be the homogametic (ZZ) sex. According to our model, intersex individuals that are functionally males are genetically females (WZ). Individual crosses were performed between intersex and female crayfish, with control crosses being performed between normal males and females. The control crosses yielded, in most cases, the expected 1:1 sex ratio in the F1 progeny. Crosses between intersex individuals and females yielded a 1:3 (male:female) sex ratio in most crosses. According to our hypothesis, one-third of the females produced in a cross of a female with an intersex animal should be WW females. The hypothesis was tested by crossing normal males with F1 females, which were progeny of intersex fathers. These crosses yielded almost 100% females, a finding that conforms to the above-suggested sex determination model for C. quadricarinatus and the female WZ genotype of intersex individuals.     

Physical-chemical features and determination of pesticides in the lagoon water in Gandoca, Limón, Costa Rica.

Nutrients and chlorophylls concentrations, as well as salinity, temperature and Secchi disk depth were determined from November 1999 to April 2000, at three stations and two depths, at Gandoca lagoon, Gandoca-Manzanillo National Wildlife Refuge, Limón, Costa Rica. Salinity profiles indicated that the lagoon was a salt wedge estuary with a partially mixed region near the mouth. No processes of eutrophication were found. The distribution and abundance of nutrients and chlorophylls showed a slight influence of continental water and water circulation patterns in the lagoon. A preliminary study was done in order to analyze the presence of 20 organochlorated and organophosphorated pesticides along the Gandoca lagoon in February 2000. None of the pesticides were detected by the analysis of residues from liquid-liquid extractions. The absence of the pesticides may be due to the fact that they did not reach the lagoon or, if they did, they were washed away by the strong rains during the sampling period.     

Genetic isolation between two sympatric host-plant races of the European corn borer,Ostrinia nubilalis Hübner. I. Sex pheromone,moth emergence timing,and parasitism

Adaptation to different environments may be a powerful source of genetic differentiation between populations. The biological traits selected in each environment can pleiotropically induce assortative mating between individuals of these genetically differentiated populations. This situation may facilitate sympatric speciation. Successful host shifts in phytophagous insects provide some of the best evidence for the ecological speciation that occurs, or has occurred, in sympatry. The European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae), colonized maize after its introduction into Europe by humans about 500 years ago. In northern France, two sympatric host races feed on maize (Zea mays) and mugwort (Artemisia vulgaris), respectively. We investigated the factors involved in the genetic isolation of these two races at a field site near Paris, France. We identified two biological differences that might make a significant contribution to the genetic divergence between sympatric populations feeding on the two host plants. First, assortative mating may be due to differences in the moth emergence pattern between the two races: mugwort-race moths emerged on average 10 days earlier than maize-race moths. In addition, the males emerged earlier than females in both races. Hence, the likelihood of mating between maize-race males and mugwort-race females was higher than that of mating between mugwort-race males and maize-race females. Second, the females feeding on mugwort and maize produced sex pheromones with different E/Z isomeric ratios of delta-11-tetradecenyl acetate. This difference in mate recognition systems reinforces the potential for assortative mating in the two races. During the experiment, overwintering mortality was much lower on maize than on mugwort. This difference was due to a braconid parasitoid wasp, Macrocentrus cingulum, that killed more than 50% of the larvae overwintering on mugwort but did not infest larvae diapausing on maize. Hence, by colonizing maize, European corn borer populations probably escaped from numerous predators, competitors, and parasitoids, such as M. cingulum. This decrease in host-associated selection may have favored the colonization of this new host. Finally, throughout this experiment we observed selection at two allozyme loci (or at linked loci): Tpi and Mpi. The Tpi locus is tightly linked with the genes involved in the response of the male to the sex pheromone and in developmental timing. The location of these traits on the Z chromosome may play a role in shortening the time required for the evolution of premating barriers.     

Sex, Death, and Evolution in Proto- and Metazoa, 1876–1913

In the period 1875–1920, a debate about the generality and applicability of evolutionary theory to all organisms was motivated by work on unicellular ciliates like Paramecium because of their peculiar nuclear dualism and life cycles. The French cytologist Emile Maupas and the German zoologist August Weismann argued in the 1880s about the evolutionary origins and functions of sex (which in the ciliates is not linked to reproduction), and death (which appeared to be the inevitable fate of lineages denied sexual conjugation), an argument rooted in the question of whether the ciliates and their processes where homologous to other cellular organisms. In the beginning of the twentieth century, this question of homology came to be less important as the ciliates were used by the British protozoologist Clifford Dobell and the American zoologist Herbert Spencer Jennings to study evolutionary processes in general rather than problems of development and cytology. For them, homology mattered less than analogy. This story illustrates two partially distinct problems in evolutionary biology: first, the question of whether all living things have common features and origins; and second, whether their history and current nature can be described by identical mechanisms. Where Maupas (contra Weismann) made the ciliates qualitatively the same as all other organisms in order to create a cohesive evolutionary theory for biology, Jennings and Dobell made them qualitatively different in order to achieve the same end. This revised version was published online in July 2006 with corrections to the Cover Date.