Tempo and Mode: Evidence on a Protracted Split From a Dense Fossil Record

Fossil records generally inform paleobiologists about extinct taxa and rates of evolution measured at the scale of millions of years. Good records that are densely sampled through time can reveal species level details such as longevity in local sections. Yet fossil data normally do not address details of lineage microevolution because the density through time of lineage sampling is insufficient to perceive patterns at a precision finer than 106 years in most cases. This study concerns details of a splitting event in the evolution of murine rodents, an event for which multiple fossil samples dated to a precision of 105 years fortuitously document the tempo and mode of origin of sister species, the stems of two extant tribes of mice. Evolution of early Murinae in the northern part of the biogeographically restricted Indian subcontinent between 11.6 and 10.5 Ma involved cladogenesis of two crown taxa, the extant tribes Murini and Arvicanthini. Large samples of fossil rodent teeth document their divergence from a common morphological pool. Definitive basal Murini and Arvicanthini at 10.5 Ma are similar in size and differ by subtle features of the dentition. Those features occur sporadically in the common pool of older fossil teeth at 11.2, 11.4, and 11.6 Ma as inconsistent polymorphisms. Interpreted as a single lineage in the 11.6–11.2 Ma interval, variability of this abundant murine incorporated the roots of the two crown tribes. The pattern through time suggests morphological stasis for several hundred thousand years prior to splitting. This special case informs us on one example of evolution and shows that the tempo of splitting evolution in some cases may be measured in hundreds of thousands of years, followed by stasis once daughter species have differentiated morphologically.

Peculiarities of microevolution processes in Trollius asiaticus in South Siberia Mountains

In the paper, we analyse the distribution of species and forms closely-related to Trollius asiaticus L. growing in the mountains of South Siberia between the Altai Mountain Country and Baikalia. The interrelationship between the endemic species and forms of high-mountains and parental lowland forms are adjacent-sympatric. We suppose the ways of disruptive selection to be of the same type, thus resulting in T. sajanensis and T. altaicus speciation, which are twin-species to each other. Between the parental and daughter species, there are interlayers of morphological forms being introgressive to both species. Key words: characters, populations, disruptive selection, introgression, speciation.

Chemical modelling of dust–gas chemistry within AGB outflows – I. Effect on the gas-phase chemistry

ABSTRACT Chemical modelling of asymptotic giant branch (AGB) outflows is typically focused on either non-thermodynamic equilibrium chemistry in the inner region or photon-driven chemistry in the outer region. We include, for the first time, a comprehensive dust–gas chemistry in our AGB outflow chemical kinetics model, including both dust–gas interactions and grain-surface chemistry. The dust is assumed to have formed in the inner region, and follows an interstellar-like dust-size distribution. Using radiative transfer modelling, we obtain dust temperature profiles for different dust types in an O-rich and a C-rich outflow. We calculate a grid of models, sampling different outflow densities, drift velocities between the dust and gas, and dust types. Dust–gas chemistry can significantly affect the gas-phase composition, depleting parent and daughter species and increasing the abundance of certain daughter species via grain-surface formation followed by desorption/sputtering. Its influence depends on four factors: outflow density, dust temperature, initial composition, and drift velocity. The largest effects are for higher density outflows with cold dust and O-rich parent species, as these species generally have a larger binding energy. At drift velocities larger than ∼10 km s−1, ice mantles undergo sputtering; however, they are not fully destroyed. Models with dust–gas chemistry can better reproduce the observed depletion of species in O-rich outflows. When including colder dust in the C-rich outflows and adjusting the binding energy of CS, the depletion in C-rich outflows is also better reproduced. To best interpret high-resolution molecular line observations from AGB outflows, dust–gas interactions are needed in chemical kinetics models.

Paraphyletic Species of Podostemaceae: Cladopus fallax and Polypleurum wallichii

All species of Podostemaceae grow only in rocky rapids and waterfalls and usually consist of separate populations. Previous studies found paraphyletic species among such species and suggested that possibly more species are paraphyletic. Molecular phylogenetic analyses and comparative morphology using samples from different populations found that Cladopus fallax C.Cusset and Polypleurum wallichii (R.Br. ex Griff.) Warm. are paraphyletic to C. taiensis C.Cusset and P. schmidtianum Warm., respectively. It is interpreted that the daughter species markedly differentiated morphologically from a population of the mother species, and perhaps paraphyletic speciation is associated with allopatric speciation. Molecular and morphological data indicate that P. wallichii is conspecific with P. stylosum (Wight) J.B.Hall, so the redefined P. wallichii is widely distributed in southern and southeastern Asia.

Monitoring of the activity and composition of comets 41P/Tuttle–Giacobini–Kresak and 45P/Honda–Mrkos–Pajdusakova

We report on photometry and imaging of the Jupiter family comets 41P/Tuttle–Giacobini–Kresak and 45P/Honda–Mrkos–Pajdusakova with the TRAPPIST-North (TRAnsiting Planets and PlanetesImals Small Telescope) telescope. We observed 41P on 34 nights from February 16 to July 27, 2017, pre- and post-perihelion (rh = 1.04 au), and collected data for comet 45P after perihelion (rh = 0.53 au) from February 10 to March 30, 2017. We computed the production rates of the daughter species OH, NH, CN, C3 and C2 and we measured the dust proxy, Afρ, for both comets. The peak of water-production rate of 41P was (3.46 ± 0.20) × 1027 molecules s−1 on April 3, 2017, when the comet was at 1.05 au from the Sun. We have shown that the activity of 41P is decreasing by about 30–40% from one apparition to the next. We measured a mean water-production rate for 45P of (1.43 ± 0.62) × 1027 molecules s−1 during a month after perihelion. Our results show that these Jupiter family comets had low gas and dust activity and no outburst was detected. Relative abundances, expressed as ratios of production rates and the Afρ parameter with respect to OH and to CN, were compared to those measured in other comets. We found that 41P and 45P have a typical composition in terms of carbon-bearing species. The study of coma features exhibited by the CN gas species allowed the measurement of the rotation period of 41P, showing a surprisingly large increase of the rotation period from (30 ± 5) h at the end of March to (50 ± 10) h at the end of April, 2017, in agreement with recent observations by other teams.

Specialization and generalization in the diversification of phytophagous insects: tests of the musical chairs and oscillation hypotheses

Evolutionary biologists have often assumed that ecological generalism comes at the expense of less intense exploitation of specific resources and that this trade-off will promote the evolution of ecologically specialized daughter species. Using a phylogenetic comparative approach with butterflies as a model system, we test hypotheses that incorporate changes in niche breadth and location into explanations of the taxonomic diversification of insect herbivores. Specifically, we compare the oscillation hypothesis, where speciation is driven by host-plant generalists giving rise to specialist daughter species, to the musical chairs hypothesis, where speciation is driven by host-plant switching, without changes in niche breadth. Contrary to the predictions of the oscillation hypothesis, we recover a negative relationship between host-plant breadth and diversification rate and find that changes in host breadth are seldom coupled to speciation events. By contrast, we present evidence for a positive relationship between rates of host switching and butterfly diversification, consonant with the musical chairs hypothesis. These results suggest that the costs of trophic generalism in plant-feeding insects may have been overvalued and that transitions from generalists to ecological specialists may not be an important driver of speciation in general.

Settling down of seasonal migrants promotes bird diversification

How seasonal migration originated and impacted diversification in birds remains largely unknown. Although migratory behaviour is likely to affect bird diversification, previous studies have not detected any effect. Here, we infer ancestral migratory behaviour and the effect of seasonal migration on speciation and extinction dynamics using a complete bird tree of life. Our analyses infer that sedentary behaviour is ancestral, and that migratory behaviour evolved independently multiple times during the evolutionary history of birds. Speciation of a sedentary species into two sedentary daughter species is more frequent than speciation of a migratory species into two migratory daughter species. However, migratory species often diversify by generating a sedentary daughter species in addition to the ancestral migratory one. This leads to an overall higher migratory speciation rate. Migratory species also experience lower extinction rates. Hence, although migratory species represent a minority (18.5%) of all extant birds, they have a higher net diversification rate than sedentary species. These results suggest that the evolution of seasonal migration in birds has facilitated diversification through the divergence of migratory subpopulations that become sedentary, and illustrate asymmetrical diversification as a mechanism by which diversification rates are decoupled from species richness.