Weak links: 'Rapoport's rule' and large-scale species richness patterns

Many hypotheses have been proposed to explain regional species richness patterns. Among these, ‘Rapoport's rule’ has sparked considerable controversy by stating that the latitudinal gradient in species richness can be explained indirectly as a function of narrower geographic ranges for species at low latitudes. Annual climatic variability, or deviation from mean climatic conditions, has been hypothesized to moderate this phenomenon. Furthermore, taxa that avoid much of this seasonality, such as temperate zone insects that enter diapause or species that migrate, were predicted to show reduced latitudinal gradients in richness. I test the suggested link between ‘Rapoport's rule’ and species richness for two higher level insect taxa as well as for the class Mammalia. Although these taxa exhibit the well-known latitudinal gradient in species richness, simple annual climatic variability and deviation from mean annual climatic conditions provide very poor predictions of species richness in each of them. Potential evapotranspiration, a measurement of ambient climatic energy, explains most of the observed variance in regional species richness patterns for all three taxa, consistent with the species richness-energy hypothesis. I find no support for an indirect link between ‘Rapoport's rule’ and terrestrial species richness patterns in North America.     

Genetic relatedness in viscous populations

Summary Hamilton's inclusive fitness rule shows that the evolution of altruism is facilitated by high genetic relatedness of altruists to their beneficiaries. But the evolution of altruism is inhibited when the beneficiaries are also close competitors of the altruist, as will often be true in structured or viscous populations. However, Hamilton's rule still gives the correct condition for the evolution of altruism if relatedness is measured with respect to the local competitive neighbourhood.     

GREENBEARDS

Greenbeards are genes that can identify the presence of copies of themselves in other individuals, and cause their bearer to behave nepotistically toward those individuals. In recent years, a number of examples have been discovered, and it has been suggested that greenbeards represent one of the fundamental routes to social behaviors such as cooperation. However, despite their possible theoretical and empirical importance, many basic aspects of greenbeard biology are commonly misunderstood. Here, we distinguish between four different types of greenbeard, which differ in their evolutionary dynamics. We show that all four types exist, and that they differ in the ease with which they can be empirically detected. We clarify the inclusive fitness explanation of greenbeards, and show that they are not intragenomic outlaws. Finally, we argue that although greenbeards are likely to be most common and easiest to detect in microorganisms, they are unlikely to important in organisms such as humans.     

A test of alternative hypotheses for kin recognition in cannibalistic tiger salamanders

The function of kin recognition is controversial. We investigatedthe adaptive significance of kin discrimination in cannibalistictiger salamander larvae, Ambystoma tigrinum. Previous laboratoryexperiments show that cannibals preferentially consume lessrelated individuals. We hypothesized that this example of kinrecognition (1) is a laboratory artifact, (2) is a by-productof sibship-specific variation in escape responses, because cannibalsfrom families with rapid responses may be more likely to cannibalize slowlyescaping non-kin, (3) is an epiphenomenon of species recognition,(4) functions in disease avoidance, because kin may be moreinfectious than non-kin, or (5) is favored by kin selection.We evaluated these five hypotheses by using laboratory and fieldexperiments to test specific predictions made by each hypothesis.We rejected hypotheses 1-4 above because (1) kin recognitionwas expressed in the wild, (2) escape responses did not reliablypredict whether a cannibal would ingest kin or non-kin, (3)kin recognition was not most pronounced in populations wheretiger salamanders co-occur with other species of salamanders,and (4) non-kin prey were more likely than kin to transmit pathogensto cannibals. However, we established that the necessary conditionfor kin selection, Hamilton's rule, was met. Thus, our resultsimplicate kin selection as the overriding reason that cannibalistictiger salamanders discriminate kin.