Countergradient variation in the sexual coloration of guppies (Poecilia reticulata): Dropsopterin synthesis balances carotenoid availability:
Limits on carotenoids in the diet force guppies to vary the amount of dropsopterin they produce. The ratio is constant across regions, so the populations may have evolved different levels of dropsopterin in response to environmental carotenoid levels. Genetic studies show that dropsopterin levels are genetically controlled. Evolution produced a testable hypothesis and that hypothesis leads to new research on mechanisms of speciation (macroevolution).
Ecological adaptation and species recognition drives vocal evolution in neotropical suboscine birds:
Evolutionary differences in mating signals, as regularly discussed here, plays a major role in speciation. The authors evaluate various hypotheses about mating system divergence, and test three. They found that closely related species living together are more divergent in song than species living apart. The environment and body size also had a significant influence on songs.
Testable predictions come from evolutionary hypotheses, and the results yield more macroevolutionary hypotheses.
Fine scale endemism on coral reefs: Archipelagic differentiation in turbinid gastropods:
Here we show that the gastropod Astralium “rhodostomum” has developed endemic clades on almost every Pacific archipelago sampled, a pattern unprecedented in marine biogeography, and reminiscent of the terrestrial biota of oceanic islands. Mitochondrial DNA sequences indicate that this species-complex is comprised of at least 30 geographically isolated clades, separated by as little as 180 km. Evidence suggests that such fine scale endemism and high diversity is not exceptional, but likely characterizes a substantial fraction of the reef biota. These results imply that (1) marine speciation can regularly occur over much finer spatial scales than generally accepted, (2) the diversity of coral reefs is even higher than suggested by morphology-based estimates, and (3) conservation efforts need to focus at the archipelagic level in the sea as on land.
New evolutionary hypotheses are tested and we increase our understanding of evolution, speciation, diversity, and conservation.
Geographical variation in the rate of evolution: Effect of available energy or fluctuating environment?Responding to a previous article, the authors feel that the tests of an evolutionary hypothesis were insufficient. Evolution leads to testable hypotheses and allows for disagreements.
Growth rate correlates to individual heterozygosity in the European eel, Anguilla anguilla L:
We provide evidence for a positive correlation between genetic variability and growth rate at 12 allozyme loci in a catadromous marine fish species, the European eel (Anguilla anguilla L.). More heterozygous individuals show a significantly higher length and weight increase and an above average condition index in comparison with more homozygous individuals.
That means genetic diversity is being selected for in these species. Evolutionary hypotheses tested.
Increased rates of molecular evolution in an equatorial plant clade: An effect of environment or phylogenetic nonindependence?Why do equatorial
Mearnsia have more rapid molecular evolution than more southerly congeners? The authors disagree with a previous paper which argued for the effect of geography. This paper finds that the effect can be explained by the common descent of the equatorial clade.
Male-by-female interactions influence fertilization success and mediate the benefits of polyandry in the sea urchin Heliocidaris erythrogramma:
Numerous studies have reported that females benefit from mating with multiple males (polyandry) by minimizing the probability of fertilization by genetically incompatible sperm. Few, however, have directly attributed variation in female reproductive success to the fertilizing capacity of sperm. In this study we report on two experiments that investigated the benefits of polyandry and the interacting effects of males and females at fertilization in the free-spawning Australian sea urchin Heliocidaris erythrogramma
Polyandry is an evolved pattern in urchins. Evolution produces testable hypotheses.
Polyandry promotes enhanced offspring survival in decorated cricketsIs a theme developing? Multiple matings in crickets mean that females leave more offspring and that those offspring survive longer. Evolutionary theory predicts that polyandry would be common under these circumstances, and it's true.
Rapid and repeated origin of insular gigantism and dwarfism in Australian tiger snakes:
Here we discriminate between two competing hypotheses with a molecular phylogeography dataset comprising approximately 4800 bp of mtDNA and demonstrate that populations of island dwarfs and giants have evolved five times independently. In each case the closest relatives of the giant or dwarf populations are mainland tiger snakes, and in four of the five cases, the closest relatives are also the most geographically proximate mainland tiger snakes. Moreover, these body size shifts have evolved extremely rapidly and this is reflected in the genetic divergence between island body size variants and mainland snakes.
In addition to the tests of evolutionary hypotheses, and the documentation of the process behind speciation, we also get insight into why some snakes get bigger, and others smaller. Small snakes are on islands with small prey, big snakes on islands with big food. This is called character displacement, a testable evolutionary hypothesis.
Rates of divergence in gene expression profiles of primates, mice, and flies: Stabilizing selection and variability among functional categoriesBy comparing two strains of lab mice, two species of fruit fly, and humans and chimps, the authors show that while genes diverge, the expression of genes is constant across time. This implies directional selection, and the divergence can be explained by short periods of directional selection. That's a lot like Gould and Eldridge's punctuated equilibrium.
Sexual selection, genetic architecture, and the condition dependence of body shape in the sexually dimorphic fly Prochyliza xanthostoma (Piophilidae)Sexual selection explains why certain characteristics of the flies respond highly to the fly's body condition, in accordance with theory.
The probability of parallell evolution:
More precisely, what is the probability that selection will cause two populations that live in identical environments to substitute the same beneficial mutation? Here I show that, under fairly general conditions, the answer is simple: if a wild-type sequence can mutate to n different beneficial mutations, replicate populations will on average fix the same mutation with probability P = 2/(n + 1).
Evolution inspires novel and testable hypotheses.
The role of Haldane's rule in sex allocation:
Sex allocation theory predicts that parents should bias their reproductive investments toward the offspring sex generating the greatest fitness return. When females are the heterogametic sex (e.g., ZW in butterflies, some lizards, and birds), production of daughters is associated with an increased risk of offspring inviability due to the expression of paternal, detrimental recessives on the Z chromosome. Thus, daughters should primarily be produced when mating with partners of high genetic quality. When female sand lizards (Lacerta agilis) mate with genetically superior males, exhibiting high MHC Class I polymorphism, offspring sex ratios are biased towards daughters, possibly due to recruitment of more Z-carrying oocytes when females have assessed the genetic quality of their partners. If our study has general applicability across taxa, it predicts taxon-specific sex allocation effects depending on which sex is the heterogametic one.
And why would the pattern hold? Evolutionary theory and common descent.
The transition to social inbred mating systems in spiders: Role of inbreeding tolerance in a subsocial predecessor:
The social spiders are unusual among cooperatively breeding animals in being highly inbred. In contrast, most other social organisms are outbred owing to inbreeding avoidance mechanisms. The social spiders appear to originate from solitary subsocial ancestors, implying a transition from outbreeding to inbreeding mating systems. Such a transition may be constrained by inbreeding avoidance tactics or fitness loss due to inbreeding depression. We examined whether the mating system of a subsocial spider, in a genus with three social congeners, is likely to facilitate or hinder the transition to inbreeding social systems. … It is likely that the lack of inbreeding avoidance in subsocial predecessors has facilitated the transition to regular inbreeding social systems.
Evolution generates testable hypotheses about macroevolutionary transitions, and their predictions are borne out.
Next up: The Journal of Mammalogy, or maybe Ecology.
