Plasticity of opsin gene expression in cichlids from Lake Malawi

Sensory systems play crucial roles in survival and reproduction. Therefore, sensory plasticity has important evolutionary implications. In this study, we examined retinal plasticity in five species of cichlid fish from Lake Malawi. We compared the cone opsin expression profiles of wild‐caught fish to lab‐reared F₁ that had been raised in a UV minus, reduced intensity light environment. All of the opsin genes that were expressed in wild‐caught fish were also expressed in lab‐reared individuals. However, we found statistically significant differences in relative opsin expression among all five species. The most consistent difference was in the SWS2B (violet) opsin, which was always expressed at higher levels in lab‐reared individuals. Estimates of visual pigment quantum catch suggest that this change in expression would increase retinal sensitivity in the light environment of the lab. We also found that the magnitude of plasticity varied across species. These findings have important implications for understanding the genetic regulation of opsin expression and raise many interesting questions about how the cichlid visual system develops. They also suggest that sensory plasticity may have facilitated the ecological diversification of cichlids in Lake Malawi.     

Male‐skewed adult sex ratio,survival, mating opportunity and annual productivity in the Snowy Plover Charadrius alexandrinus

Sex differences in adult mortality may be responsible for male‐skewed adult sex ratios and male‐skewed parental care in some birds. Because a surplus of breeding males has been reported in serially polyandrous populations of Snowy Plover Charadrius alexandrinus, we examined sex ratio, early‐season nesting opportunities, adult survival and annual reproductive success of a Snowy Plover population at Monterey Bay, California. We tested the hypotheses that male adult survival was greater than female survival and that a sex difference in adult survival led to a skewed adult sex ratio, different mating opportunities and different annual productivity between the sexes. Virtually all females left chicks from their first broods to the care of the male and re‐nested with a new mate. As a result, females had time to parent three successful nesting attempts during the lengthy breeding season, whereas males had time for only two successful attempts. Among years, the median population of nesting Plovers was 96 males and 84 females (median difference = 9), resulting in one extra male per eight pairs. The number of potential breeders without mates during the early nesting period each year was higher in males than in females. Adult male survival (0.734 ± 0.028 se) was higher than female survival (0.693 ± 0.030 se) in top‐ranked models. Annually, females parented more successful clutches and fledged more chicks than their first mates of the season. Our results suggest that in C. alexandrinus a sex difference in adult survival results in a male‐skewed sex ratio, which creates more nesting opportunities and greater annual productivity for females than for males.     

Species limits within the Praomys delectorum group (Rodentia: Muridae: Murinae) of East Africa: a morphometric reassessment and biogeographical implications

We examined approximately 600 specimens that represent the Praomys delectorum species group (Muridae: Murinae: Praomyini), a rodent complex restricted to Afromontane landscapes in East Africa and currently viewed as a single species. Morphometric analyses of 21 population samples consistently disclosed cohesive patterns of craniodental differentiation that support the recognition of three species: Praomys delectorum Thomas, confined to extreme southern Malawi; P. melanotus Allen & Loveridge, found in highlands of south‐western Tanzania and contiguous northern Malawi; and P. taitae Heller (including octomastis Hatt), distributed in mountains and foothills of southern Kenya and northern and central Tanzania. Populations of the P. delectorum group are patchily distributed in moist montane forest, most collecting localities falling within 1000–2400 m, and their range collectively coincides with the Tanganyika–Nyasa Montane Forest Group sensu Moreau. Patterns of faunal similarity derived from distributions of 65 species of terrestrial small mammals recorded from Tanzania's highlands, including the Eastern Arc Mountains, demonstrated pronounced geographical discontinuities in montane associations but failed to uncover a prominent vicariant role for the Makambako Gap. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 420–469.     

Mortality and Self-thinning in Postfire Black Spruce

Using age-structure determinations on both living and dead stemsin censused plots, coupled with stem analysis techniques, anhistorical picture of mortality and above-ground tree stem growthwas recreated for ten stands dominated by black spruce in northeasternOntario, Canada. No evidence of mortality was seen in any plot prior to 30 yearsfollowing postfire initiation. Each of the eight oldest standsshowed a linear decline in numbers for a 20–25 year period.The steepness of the mortality slope was proportional to initiallive stem density within and among plots during this phase.The final 10–20 years was marked by a less steep declinein numbers. The log density vs log mean tree volume curves in the eightoldest stands were doubly asymptotic and were fitted to a logisticcurve very tightly in each case. At the point of inflectionthe curves' slopes ranged from –2.14 to –3.89. However,log density vs log mean stem volume among stands at this pointof inflection had a slope of –0.96. Reasons for the inconsistency between within-stand and among-standself-thinning estimates are considered, as well as the poorfit to the –3/2 rule. Ecosystem processes related to thechange in nutrient relations during stand growth are identifiedas a prime influence on self-thinning behaviour in natural blackspruce stands. Mortality, stem analysis, self-thinning, Picea mariana, black spruce