Ecology and genetics of speciation in Ficedula flycatchers

Birds have for long been popular study objects in speciation research. Being easy to observe in the field, they have traditionally been particularly important in studies of behavioural and ecological factors in speciation, whereas the genetic aspects of the process have been studied in other organisms, such as Drosophila. More recently, however, a stronger genetic focus has been placed on speciation research also in birds. Here, we review ecological, behavioural and genetic studies on speciation in the pied flycatcher (Ficedula hypoleuca) and the collared flycatcher (Ficedula albicollis). These well‐studied birds provide among the few proposed examples of the process of reinforcement of premating isolation, and the evidence for reinforcement is strong. They are further characterized by having strong intrinsic postzygotic barriers (female hybrid sterility), yet the two species appear to be very similar ecologically. This is in stark contrast to another well‐studied bird complex, Darwin’s finches, in which the species differ vastly in ecologically important traits but have no developmental problems arising from genetic incompatibilities, and where no evidence for reinforcement is found. In the flycatchers, sex chromosome linkage of genes affecting traits associated with both pre‐ and postzygotic barriers to gene exchange is likely to facilitate reinforcement. We discuss whether such sex‐linkage may be common in birds. The contrast between flycatchers and Darwin’s finches indicate that speciation in birds cannot always be understood mainly as a result of divergent natural selection (‘ecological speciation’), and generalizations from one system may lead us astray. We discuss to what extent insight from research on the flycatchers may point to fruitful avenues for future research on bird speciation and specifically call for a more systematic effort to simultaneously investigate ecology, behaviour and genetics of birds caught in the process of speciation.     

Hybrid speciation in sparrows II: a role for sex chromosomes?

Homoploid hybrid speciation in animals is poorly understood, mainly because of the scarcity of well‐documented cases. Here, we present the results of a multilocus sequence analysis on the house sparrow (Passer domesticus), Spanish sparrow (P. hispaniolensis) and their proposed hybrid descendant, the Italian sparrow (P. italiae). The Italian sparrow is shown to be genetically intermediate between the house sparrow and Spanish sparrow, exhibiting genealogical discordance and a mosaic pattern of alleles derived from either of the putative parental species. The average variation on the Z chromosome was significantly reduced compared with autosomal variation in the putative parental species, the house sparrow and Spanish sparrow. Additionally, divergence between the two species was elevated on the Z chromosome relative to the autosomes. This pattern of variation and divergence is consistent with reduced introgression of Z‐linked genes and/or a faster‐Z effect (increased rate of adaptive divergence on the Z). F_ST‐outlier tests were consistent with the faster‐Z hypothesis: two of five Z‐linked loci (CHD1Z and PLAA) were identified as candidates for being subject to positive, divergent selection in the putative parental species. Interestingly, the two latter genes showed a mosaic pattern in the (hybrid) Italian sparrow; that is, the Italian sparrow was found to be fixed for Spanish sparrow alleles at CHD1Z and to mainly have house sparrow alleles at PLAA. Preliminary evidence presented in this study thus suggests that sex chromosomes may play a significant role in this case of homoploid hybrid speciation.     

Effects of climate on population fluctuations of ibex

Predicting the effects of the expected changes in climate on the dynamics of populations require that critical periods for climate‐induced changes in population size are identified. Based on time series analyses of 26 Swiss ibex (Capra ibex) populations, we show that variation in winter climate affected the annual changes in population size of most of the populations after accounting for the effects of density dependence and demographic stochasticity. In addition, precipitation during early summer also influenced the population fluctuations. This suggests that the major influences of climate on ibex population dynamics operated either through loss of individuals during winter or early summer, or through an effect on fecundity. However, spatial covariation in these climate variables was not able to synchronize the population fluctuations of ibex over larger distances, probably due to large spatial heterogeneity in the effects of single climate variables on different populations. Such spatial variation in the influence of the same climate variable on the local population dynamics suggests that predictions of influences of climate change need to account for local differences in population dynamical responses to climatic conditions.     

Buchonomyia burmanica sp.n. and Buchonomyiinae, a New Subfamily among the Chironomidae (Diptera)

Male and female imagines of Buchonomyia burmanica sp.n. are described. While the male imago nearly exclusively shows plesiomorphous features, the female imago possesses three important underlying synapomorphies as unique inside-parallelisms: the capacities for divisions of gonapophysis VIII and of tergite IX and for the development of an apodeme lobe. These and supporting evidence lead to the conclusion that Buchonomyia Fittkau deserves a new subfamily, the Buchonomyiinae, which forms the sister-group of the monophyletic unit Chironominae-t-Orthocladiinae+Prodiamesinae+Diamesinae.     

Hybrid speciation in sparrows I: phenotypic intermediacy,genetic admixture and barriers to gene flow

Homoploid hybrid speciation is thought to require unusual circumstances to yield reproductive isolation from the parental species, and few examples are known from nature. Here, we present genetic evidence for this mode of speciation in birds. Using Bayesian assignment analyses of 751 individuals genotyped for 14 unlinked, nuclear microsatellite loci, we show that the phenotypically intermediate Italian sparrow (Passer italiae) does not form a cluster of its own, but instead exhibits clear admixture (over its entire breeding range) between its putative parental species, the house sparrow (P. domesticus) and the Spanish sparrow (P. hispaniolensis). Further, the Italian sparrow possesses mitochondrial (mt) DNA haplotypes identical to both putative parental species (although mostly of house sparrow type), indicating a recent hybrid origin. Today, the Italian sparrow has a largely allopatric distribution on the Italian peninsula and some Mediterranean islands separated from its suggested parental species by the Alps and the Mediterranean Sea, but co‐occurs with the Spanish sparrow on the Gargano peninsula in southeast Italy. No evidence of interbreeding was found in this sympatric population. However, the Italian sparrow hybridizes with the house sparrow in a sparsely populated contact zone in the Alps. Yet, the contact zone is characterized by steep clines in species‐specific male plumage traits, suggesting that partial reproductive isolation may also have developed between these two taxa. Thus, geographic and reproductive barriers restrict gene flow into the nascent hybrid species. We propose that an origin of hybrid species where the hybrid lineage gets geographically isolated from its parental species, as seems to have happened in this system, might be more common in nature than previously assumed.     

Underlying Synapomorphies and Anagenetic Analysis

Evaluations of holomorphological similarities are based on synapomorphies, symplesiomorphies, convergence, and parallelisms as results of parallel selection and of underlying synapomorphies respectively. Only synapomorphies and underlying synapomorphies can show genealogical relationships. Distinctions between parallel selections and underlying synapomorphies are of major phylogenetic importance, while distinctions between different evolutionary histories (eu-parallelisms and pseudo-parallelisms) are not. The circumstance when underlying synapomorphies are of special phylogenetic importance has been termed unique inside-parallelism. Three such unique inside-parallelisms are found in the female genitalia of the Chironomidae, where they are shown necessary for the understanding of subfamily relationships. — The first minimum criterion for recognizing synapomorphy (Schlee 1971) is corrected to: It should be present within the whole group or clearly secondarily reduced an apomorphic taxa. It should not be present in the same formation in any taxon outside the group which can be regarded as a possible sister group. — The anagenetic component of the evolutionary processes can, following a cladistic analysis, be calculated by means of the adjusted evolution index assigning the different recognizable steps of trends or morphocline number from 1 to 2 and calculating the arithmetic mean of all numbers. Examples from Chaoboridae and Chironomidae support the cladistic diagrams and point out that different stages belong to differing "grades". Methods of numerical taxonomy may give a finer gradation of anagenetic levels.     

THE MYTH OF OBJECTIVITY—POST-HENNIGIAN DEVIATIONS

Abstract— The punctuated equilibrium speciation mode is an implied consequence of the deviation rule and the differences between cladograms and phylogenetic trees implicitly were recognized by Hennig. Neocladism and transformed cladism, however, both are contradictory to the view of Hennig. Neither of them will be consistent when parallel changes exceed informative unparallel changes, which in the real world there are many indications to believe they do. In three tables cladogenetic trends used in erecting three schemes of argumentation, on the specific, generic, and subfamily levels respectively, are analyzed and divided into: " objective" synapomorphies not allowing for outside parallelism or secondary change, subjective synapomorphies , and underlying synapomorphies . Evaluations based on the strictest criteria for asserting synapomorphy are possible only when comparing higher taxa of subfamily level and up. On the generic level trends showing outside parallelism can be rejected if all other possibly synapomorphic trends are included. On the specific level it is necessary to take all kinds of synapomorphies into consideration, including those showing outside parallelism. There may often be a preponderance of trends caused by parallel selection in taxa with specialized sexual and/or feeding behaviors, as exemplified by some chironomid male imagines and larvae. It is necessary to have knowledge of the nature of the different possible natural processes and try to explain these before undertaking estimations of patterns of kinship. The persistent intuitive and subjective element in phylogenetics was stressed by Hennig. Objectivity is a myth.