Spatially varying selection shapes life history clines among populations of Drosophila melanogaster from sub-Saharan Africa.

Clines in life history traits, presumably driven by spatially varying selection, are widespread. Major latitudinal clines have been observed, for example, in Drosophila melanogaster, an ancestrally tropical insect from Africa that has colonized temperate habitats on multiple continents. Yet, how geographic factors other than latitude, such as altitude or longitude, affect life history in this species remains poorly understood. Moreover, most previous work has been performed on derived European, American and Australian populations, but whether life history also varies predictably with geography in the ancestral Afro-tropical range has not been investigated systematically. Here, we have examined life history variation among populations of D. melanogaster from sub-Saharan Africa. Viability and reproductive diapause did not vary with geography, but body size increased with altitude, latitude and longitude. Early fecundity covaried positively with altitude and latitude, whereas lifespan showed the opposite trend. Examination of genetic variance-covariance matrices revealed geographic differentiation also in trade-off structure, and QST -FST analysis showed that life history differentiation among populations is likely shaped by selection. Together, our results suggest that geographic and/or climatic factors drive adaptive phenotypic differentiation among ancestral African populations and confirm the widely held notion that latitude and altitude represent parallel gradients.

Finding of male-killing Spiroplasma infecting Drosophila melanogaster in Africa implies transatlantic migration of this endosymbiont.

We report the identification of male-killing Spiroplasma in a wild-caught female Drosophila melanogaster from Uganda, the first such infection to be found in this species outside of South America. Among 38 female flies collected from Namulonge, Uganda in April, 2005, one produced a total of 41 female offspring but no males. PCR testing of subsequent generations revealed that females retaining Spiroplasma infection continued to produce a large excess of female progeny, while females that had lost Spiroplasma produced offspring with normal sex ratios. Consistent with earlier work, we find that male-killing and transmission efficiency appear to increase with female age, and we note that males born in sex ratio broods display much lower survivorship than their female siblings. DNA sequence comparisons at three loci suggest that this Spiroplasma strain is closely related to the male-killing strain previously found to infect D. melanogaster in Brazil, although part of one locus appears to show a recombinant history. Implications for the origin and history of male-killing Spiroplasma in D. melanogaster are discussed.

An experiment on cognitive remediation of word-reading difficulty.

Cognitive remediation of decoding deficit was attempted by following a theoretically based program. The theory identifies four major cognitive processes: Planning, Attention, Simultaneous, and Successive (PASS) processing. The PASS Remedial Program (PREP) provides 10 structured tasks that are aimed at developing internalized strategies for mainly successive processes (6 tasks) and simultaneous process (4 tasks); deficits in either of the two may lead to poor decoding. Through its "global process" training and curriculum-related "bridging" training, PREP facilitates application of internalized strategies arrived at inductively for learning word decoding and spelling; it does not provide direct teaching of rules or exercises. To test the efficacy of PREP, we divided 51 children with decoding difficulties in Grade 4 into two groups: PREP (both global and bridging) and no treatment. In the second part of the study, children from the no-treatment group received either the global or the bridging part of PREP. The relative efficacy of training was tested by pre-, and posttests of performance on a standard word-decoding test (the WRMT-R), as well as on some cognitive tests (e.g., the CAS). The largest improvement in word decoding occurred for the PREP combined global and bridging treatment. The mechanism through which PREP improves word reading is discussed, as is the use of PREP for children at risk of developing dyslexia.