Through thick and thin: cryptic sympatric speciation in the submersed genus Najas (Hydrocharitaceae).

Cryptic sympatric species arise when reproductive isolation is established in sympatry, leading to genetically divergent lineages that are highly similar morphologically or virtually indistinguishable. Although cryptic sympatric species have been reported in various animals, fungi, and protists, there are few compelling examples for plants. This investigation presents a case for cryptic sympatric speciation in Najas flexilis, a widespread aquatic plant, which extends throughout northern North America and Eurasia. The taxon is noted for its variable seed morphology, which earlier research associated with cytotypes; i.e., diploids were characterized by thicker seeds and tetraploids by thinner seeds. However, cytotypes are not patterned geographically with diploid and tetraploid plants often found in close proximity within the same lake. Using digital image and DNA sequence analyses, we found that diploids and tetraploids are well-isolated and remain genetically distinct throughout their sympatric range, where sterile hybrids occur frequently. Incorporation of sequence data from the single-copy nuclear phytoene desaturase locus revealed further that the tetraploids are allopolyploid derivatives of N. flexilis and N. guadalupensis, the latter a closely related species with an overlapping distribution. We conclude that the taxon widely known as N. flexilis actually comprises two cryptic, sibling species, which diverged in sympatry by interspecific hybridization and subsequent chromosomal isolation. By comparing seed morphology of type specimens, we associated the names N. flexilis and N. canadensis to the diploids and tetraploids respectively. Additionally, the narrowly restricted taxon known formerly as N. muenscheri is shown via morphological and genetic evidence to be synonymous with N. canadensis.

A culture of future planning: perceptions of sexual risk among educated young adults.

In this study we examined how social processes, specifically the acquisition of postsecondary education and capital, shaped perceptions of sexual risk and impacted sexual practices and sexual health among young adults. Using qualitative research methods we collected and analyzed data among students attending a 4-year university in the northeastern region of the United States over a 1-year period. By analyzing participants' narratives, we found that the reproduction of shared norms and values encouraged educated young adults to focus on educational and professional success, pressing many of them to be concerned about preventing pregnancy rather than preventing disease transmission, and increasing their risk for sexually transmitted infections, including HIV/AIDS. Sexual-health educators need to address how social processes shape sexual practices, encourage educated young adults to challenge unequal gender expectations, and consider how sexually transmitted infections might also interfere with life plans.