Evolutionary genetics: The economics of mutation.

The presence of mutator genotypes in populations of bacteria may be favoured by selection because they produce rare beneficial mutations and thereby increase the rate of adaptive evolution. Recent work, however, shows that the relationship between mutation rates and adaptive evolution is more complicated.     

Evolutionary genetics: evolution with foresight

Evolution has no foresight, but produces ad hoc solutions by tinkering with available variation. A new study demonstrates how evolution nevertheless prepares organisms for the future by increasing their evolvability.     

Evolutionary genetics: choosing to evolve

The evolution of mate choice is believed to be important in speciation. A recent experiment involving mating preference evolution in laboratory yeast populations supports theoretical predictions that this can occur without complete genetic isolation between populations, strengthening the case that ecological specialization as well as physical separation can lead to speciation.     

Evolutionary genetics ofDrosophila esterases

Over 30 carboxylester hydrolases have been identified inD. melanogaster. Most are classified as acetyl, carboxyl or cholinesterases. Sequence similarities among most of the carboxyl and all the cholinesterases so far characterised fromD. melanogaster and other eukaryotes justify recognition of a carboxyl/cholinesterase multigene family. This family shows minimal sequence similarities with other esterases but crystallographic data for a few non-drosophilid enzymes show that the family shares a distinctive overall structure with some other carboxyl and aryl esterases, so they are all put in one superfamily of / hydrolases. Fifteen esterase genes have been mapped inD. melanogaster and twelve are clustered at two chromosomal sites. The constitution of each cluster varies acrossDrosophila species but two carboxyl esterases in one cluster are sufficiently conserved that their homologues can be identified among enzymes conferring insecticide resistance in other Diptera. Sequence differences between two other esterases, the EST6 carboxyl esterase and acetylcholinesterase, have been interpreted against the consensus super-secondary structure for the carboxyl/cholinesterase multigene family; their sequence differences are widely dispersed across the structure and include substantial divergence in substrate binding sites and the active site gorge. This also applies when EST6 is compared across species where differences in its expression indicate a difference in function. However, comparisons within and among species where EST6 expression is conserved show that many aspects of the predicted super-secondary structure are tightly conserved. Two notable exceptions are a pair of polymorphisms in the substrate binding site of the enzyme inD. melanogaster. These polymorphisms are associated with differences in substrate interactions_vitro} and demographic data indicate that the alternative forms are not selectively equivalentin vivo.     

Evolutionary genetics: sex happens in Giardia

Previous analyses of the Giardia genome exposed numerous genes required for meiosis, suggesting that sexual reproduction is occurring in this early-diverging eukaryote. A new study now uncovers direct genetic evidence for recombination in Giardia populations.     

Evolutionary genetics: how flies get naked

Researchers studying evolution of 'naked' (hairless) larval cuticle in Drosophila sechellia have discovered surprising complexity in the pattern of cis-regulatory differences that differentiate this species from its 'hairy' ancestors.     

Evolutionary genetics of birds IV rates of protein divergence in waterfowl (Anatidae)

An electrophoretic comparison of proteins in 26 species of waterfowl (Anatidae), representing two major subfamilies and six subfamilial tribes, led to the following major conclusions: (1) the genetic data, analyzed phenetically and cladistically, generally support traditional concepts of evolutionary relationships, although some areas of disagreement are apparent; (2) species and genera within Anatidae exhibit smaller genetic distances at protein-coding loci than do most non-avian vertebrates of equivalent taxonomic rank; (3) the conservative pattern of protein differentiation in Anatidae parallels patterns previously reported in Passeriforme birds. If previous taxonomic assignments and ages of anatid fossils are reliable, it would appear that the conservative levels of protein divergence among living species may not be due to recent age of the family, but rather to a several-fold deceleration in rate of protein evolution relative to non-avian vertebrates. Since it now appears quite possible that homologous proteins can evolve at different rates in different phylads, molecular-based conclusions about absolute divergence times for species with a poor fossil record should remain appropriately reserved. However, the recognition and study of the phenomenon of apparent heterogeneity in rates of protein divergence across phylads may eventually enhance our understanding of molecular and organismal evolution.     

Reproductive traits: evidence for sexually selected sperm

Sperm exhibit extraordinary morphological divergence yet precise evolutionary causes often remain elusive. A quantitative genetic study sheds light on the major role postcopulatory sexual selection could play in determining sperm size.     

Evolutionary genetics of ruminant lysozymes

Comparative studies of mammalian lysozymes and their genes have contributed to knowledge of how new functions arise during evolution. The recruitment of lysozymes for functioning in the stomach fluid of ruminants has occurred in response to selection pressures that are partly known and on a time-scale that is known. A semiquantitative analysis of adaptive evolution is thus made possible by the ruminant lysozyme system. Large-scale production of lysozyme by the stomach lining entailed gene duplication as well as a change in gene expression. Remoulding of the lysozyme for working and lasting in the stomach fluid involved accelerated amino acid replacements, which may have been facilitated by intergenic recombination. The possibility that multigene families can accelerate adaptive evolution, by virtue of their capacity for bringing together functionally coupled substitutions, receives emphasis in this review.     

Evolutionary genetics of plant adaptation

Plants provide unique opportunities to study the mechanistic basis and evolutionary processes of adaptation to diverse environmental conditions. Complementary laboratory and field experiments are important for testing hypotheses reflecting long-term ecological and evolutionary history. For example, these approaches can infer whether local adaptation results from genetic tradeoffs (antagonistic pleiotropy), where native alleles are best adapted to local conditions, or if local adaptation is caused by conditional neutrality at many loci, where alleles show fitness differences in one environment, but not in a contrasting environment. Ecological genetics in natural populations of perennial or outcrossing plants can also differ substantially from model systems. In this review of the evolutionary genetics of plant adaptation, we emphasize the importance of field studies for understanding the evolutionary dynamics of model and nonmodel systems, highlight a key life history trait (flowering time) and discuss emerging conservation issues.     

The quantitative genetics of sexually selected traits,preferred traits and preference: a review and analysis of the data

The maintenance of variation in sexually selected traits is a puzzle that has received increasing attention in the past several decades. Traits that are related to fitness, such as life‐history or sexually selected traits, are expected to have low additive genetic variance (and hence, heritability) due to the rapid fixation of advantageous alleles. However, previous analyses have suggested that the heritabilities of sexually selected traits are on average higher than nonsexually selected traits. We show that the heritabilities of sexually selected traits are not significantly different from those of nonsexually selected traits overall or when separated into the three trait categories: behavioural, morphological and physiological. In contrast with previous findings, the heritability of preference is quite low (h² = 0.25 ± 0.06) and is in the same range as life‐history traits. We distinguish preferred traits as a category of sexually selected traits and find that the heritability of the former is not significantly different than sexually selected traits overall (0.48 ± 0.04 vs. 0.46 ± 0.03). We test the hypothesis that the heritability of sexually selected traits is negatively correlated with the strength of sexual selection. As predicted, there is a significant negative correlation between the heritabilities of sexually selected traits and the strength of selection. This suggests that heritabilities do indeed decrease as sexual selection increases but sexual selection is not strong enough to cause heritabilities of sexually selected traits to deviate from the same type of nonsexually selected traits.