Temperature sensitivity of chromosomal polymorphism inDrosophila pseudoobscura

Population cages ofDrosophila pseudoobscura with the gene arrangements Arrowhead and Chiricahua (CH) were studied at 15 1/2°, 17 1/2°, 19°, 22°C, and a fluctuating temperature (F°) ranging from 17° to 27° with mean of 22°. At the three lower temperatures there were only small but detectable changes in the frequency of CH, but at 22° and F° the earlier populations (V and K) showed the elimination of CH and the later ones (W and L) showed an equilibrium similar to that at 25°. Evidence is presented to show that an environmental change strongly affecting population size need have no effect on the inversion system. Several environmental factors that could have influenced the results are discussed.The temperature sensitivity of the inversion system is discussed in relation toWright's adaptive surface model of genotypes. It is proposed that at about 22° there are a number of narrowly separated steep-sided peaks, some of which represent polymorphic and others monomorphic genetic systems. At 25° the surface has a single peak favoring inversion polymorphism, while from 15° to 19° no well-defined peaks are discernible.Dedicated to Prof. L. C. Dunn in friendship and in recognition of his many contributions to the science of genetics.National Science Foundation (U.S.A.) Predoctoral Fellow, 1956–1959; Columbia University Fellow, 1959–1960; Boese Postdoctoral Fellow, Columbia University, 1961–1962.     

The size at reproduction of canopy tree species in central Africa

Size at reproduction is a key aspect of species life history that is relatively understudied for long‐lived tropical trees. Here, we quantified reproductive diameter for 31 major timber species across 11 sites in Cameroon, Congo, and Central African Republic. Specifically, we examined whether (1) between‐species variability is correlated with other species traits; (2) reproductive diameter varies within‐species among sites; (3) reproductive status varies with crown exposure; and (4) the minimum cutting diameter limits (MCDL) imposed by national forest regulations enable seed trees to persist after logging operations. Consistent with studies conducted elsewhere in the tropics, we found great variability in diameter at reproduction among species, which correlated with adult stature (maximum diameter and height). For some species, reproductive diameter thresholds substantially varied between sites, and crown exposure had a significant positive effect on reproductive status. Most MCDLs were found to be suitable, with trees having a high probability of being seed trees at MCDL. Our findings have implications for the sustainable management of production forests, and they highlight questionable MCDLs for some species and between‐site variation in reproductive diameter. The study also highlights the need for long‐term phenological monitoring of tree species spanning a large range of ecological strategies to address both theoretical (species life history, allocation trade‐offs) and practical questions (MCDL).     

Population distribution,host-switching,and chemical sensing in the symbiotic shrimp <Emphasis Type="Italic">Lysmata pederseni</Emphasis>: implications for its mating system in a changing reef seascape

Lysmata pederseni, a protandric simultaneously hermaphroditic shrimp that inhabits the tube sponge Callyspongia vaginalis, is monogamous in the central and southeastern Caribbean Sea. We tested the null hypothesis of monogamy in a northern Caribbean population. In the Florida Keys, shrimps did not inhabit host individuals in pairs with a frequency greater than expected by chance alone. Hermaphrodites inhabited sponges solitarily and often brooded embryos. Hermaphrodites do not store sperm and need to be inseminated shortly after molting to fertilize a new batch of eggs. Thus, males and/or other hermaphrodites are likely switching among host individuals in search of sexual partners. Field experiments demonstrated low shrimp host fidelity. Host residence time was ~2 times shorter for males than for hermaphrodites. We inferred a polygynandrous mating system in L. pederseni from the Florida Keys, with male-role and young hermaphrodites often moving among sponges in search of older, more sedentary, female-role hermaphrodites. We expected shrimps to use water-borne chemical cues originating from conspecifics or sponges to locate sexual partners. Experiments demonstrated that shrimps were attracted to water-borne cues originating from sponges but not conspecifics. We have described the mating system of a reef-associated shrimp in a fast-pace shifting seascape increasingly dominated by sponges and vanishing stony corals. In the central and southeastern Caribbean Sea, with greater coral cover and lower sponge abundance than in the Florida Keys, the same species is monogamous. Whether or not similar shifts in the social organization of other coral reef-dwelling marine organisms are occurring due to contemporary changes in seascapes is a relevant topic that deserves further attention.