Speciation: Frog Mimics Prefer Their Own

SummaryRanitomeya poison frogs in the Peruvian Amazon are a rare example of Müllerian mimicry in vertebrates. These frogs also prefer to court same-coloured mimics. This suggests that divergence in mimicry plays a role in reproductive isolation

A Night Out with the Nerds

Simon Singh and Richard Wiseman draw on examples from physics to psychology, to explore the extraordinary in the ordinary in their innovative new play Theatre of Scienc

Snakes: Oriented families of periodic orbits, their sources, sinks, and continuation

AbstractPoincaré observed that for a differential equation x′ = ƒ(x, α) depending on a parameter α, each periodic orbit generally lies in a connected family of orbits in (x, α)-space. In order to investigate certain large connected sets (denoted Q) of orbits containing a given orbit, we introduce two indices: an orbit index φ and a “center” index defined at certain stationary points. We show that genetically there are two types of Hopf bifurcation, those we call “sources” ( = 1) and “sinks” ( = −1). Generically if the set Q is bounded in (x, α)-space, and if there is an upper bound for periods of the orbits in Q, then Q must have as many source Hopf bifurcations as sink Hopf bifurcations and each source is connected to a sink by an oriented one-parameter “snake” of orbits. A “snake” is a maximal path of orbits that contains no orbits whose orbit index is 0. See Fig. 1.1

Sympatric speciation by allochrony?

Sympatric speciation was once thought most improbable, but careful study of some systems, particularly the apple maggot (Rhagoletis pomonella) and related Rhagoletis species, has led to its reinstatement as a likely mode of speciation in some cases. Different species and host races in this clade of flies often have highly specialized host preference, and along with frequent evolutionary shifts to different fruit species between sister taxa, there is a likely effect of the timing of adult emergence that follows host fruiting phenology. This is known as “allochronic” isolation (from the Greek meaning “different timing”). This overview covers recent discoveries by Inskeep et al. (Molecular Ecology, 2021) showing how allochrony is a major factor in preventing gene flow between a pair of sister species of Rhagoletis on different host fruits. Although the authors do not claim to prove sympatric speciation, it does seem very likely, and the work clearly underscores how readily host shifts via allochrony can aid sympatric speciation

Evolution: Mimicry meets the mitochondrion

AbstractA recent molecular study of the evolution of mimicry in tropical butterflies of the genus Heliconius proves that the mimics adapted to previously diverged ‘model’ species, but does not clearly distinguish between opposing views of how the model species diverged

New genomes clarify mimicry evolution

For over 100 years, it has been known that polymorphic mimicry is often switched by simple mendelian factors, yet the physical nature of these loci had escaped characterization. Now, the genome sequences of two swallowtail butterfly (Papilio) species have enabled the precise identification of a locus underlying mimicry, adding to unprecedented recent discoveries in mimicry genetics.Organismic and Evolutionary Biolog

Admixture of evolutionary rates across a butterfly hybrid zone

Hybridization is a major evolutionary force that can erode genetic differentiation between species, whereas reproductive isolation maintains such differentiation. In studying a hybrid zone between the swallowtail butterflies Papilio syfanius and Papilio maackii (Lepidoptera: Papilionidae), we made the unexpected discovery that genomic substitution rates are unequal between the parental species. This phenomenon creates a novel process in hybridization, where genomic regions most affected by gene flow evolve at similar rates between species, while genomic regions with strong reproductive isolation evolve at species-specific rates. Thus, hybridization mixes evolutionary rates in a way similar to its effect on genetic ancestry. Using coalescent theory, we show that the rate-mixing process provides distinct information about levels of gene flow across different parts of genomes, and the degree of rate-mixing can be predicted quantitatively from relative sequence divergence (FST ) between the hybridizing species at equilibrium. Overall, we demonstrate that reproductive isolation maintains not only genomic differentiation, but also the rate at which differentiation accumulates. Thus, asymmetric rates of evolution provide an additional signature of loci involved in reproductive isolation

Full‐likelihood genomic analysis clarifies a complex history 2 of species divergence and introgression: the example of the 3 erato‐sara group of Heliconius butterflies

Introgressive hybridization plays a key role in adaptive evolution and species diversification in many groups of species. However, frequent hybridization and gene flow between species make estimation of the species phylogeny and key population parameters challenging. Here, we show that by accounting for phasing and using full-likelihood methods, introgression histories and population parameters can be estimated reliably from whole-genome sequence data. We employ the multispecies coalescent (MSC) model with and without gene flow to infer the species phylogeny and cross-species introgression events using genomic data from six members of the erato-sara clade of Heliconius butterflies. The methods naturally accommodate random fluctuations in genealogical history across the genome due to deep coalescence. To avoid heterozygote phasing errors in haploid sequences commonly produced by genome assembly methods, we process and compile unphased diploid sequence alignments and use analytical methods to average over uncertainties in heterozygote phase resolution. There is robust evidence for introgression across the genome, both among distantly related species deep in the phylogeny and between sister species in shallow parts of the tree. We obtain chromosome-specific estimates of key population parameters such as introgression directions, times and probabilities, as well as species divergence times and population sizes for modern and ancestral species. We confirm ancestral gene flow between the sara clade and an ancestral population of Heliconius telesiphe, a likely hybrid speciation origin for Heliconius hecalesia, and gene flow between the sister species Heliconius erato and Heliconius himera. Inferred introgression among ancestral species also explains the history of two chromosomal inversions deep in the phylogeny of the group. This study illustrates how a full-likelihood approach based on the MSC makes it possible to extract rich historical information of species divergence and gene flow from genomic data. [3S; BPP; gene flow; Heliconius; hybrid speciation; introgression; inversion; multispecies coalescent