Speciation

Reynolds, S. C. (2007a). Temporal variation in Plio-Pleistocene Antidorcas (Mammalia: Bovidae) horncores: the case from Bolt’s Farm and why size matters South African Journal of Science Volume 103:47-50.

by Sally Reynolds

Morphological differences in samples of fossil (Antidorcas recki)
and modern (A. marsupialis) springbok horncores... more Morphological differences in samples of fossil (Antidorcas recki)
and modern (A. marsupialis) springbok horncores suggest that the ancestral species shows less sexual dimorphism than is observed in the horn dimensions of modern springbok. This pattern may prove useful when evaluating lossil springbok specimens in South African Pfio-Pleistocene faunal assemblages. Undated Antidorcas craniodental specimens from Pit 3, Bolt's Farm (Cradle of Humankind, Gauteng, South Africa) have previously been referred to A. recki by Cooke. However, comparison with numerous other springbok samples suggests that these specimens are more likely to represent male and lemale fossils of the extant species, A. marsupialis. This re-evaluationa dds weight to the fossil evidence implying that the modern form of springbok is a southern Alrican endemic species which first appeared around 1.5-1.0 million years ago in Swartkrans Member 1. Bolt's Farm Pit 3 fossils are inferred
to be of a similar age.

Trace metal cycling in the Whau Estuary, Auckland, New Zealand

by Peter Wilson

The evolutionary history of Fagus in western Eurasia: Evidence from genes, morphology and the fossil record.

by Guido Grimm

Authored by Denk, Grimm, Stögerer, Langer, Hemleben

Fagus (beech) is among the most abundant and economically important genera of broadleaved trees in northern hemisphere... more Fagus (beech) is among the most abundant and economically important genera of broadleaved trees in northern hemisphere temperate forests. The number of modern taxa present in Europe and Asia Minor has long been a matter of debate and up to five species have been recognised. To resolve taxonomic and phylogenetic relationships we conducted morphological and molecular genetic analyses in western Eurasiatic taxa and evaluated palaeontological evidence. To place our findings from western Eurasiatic populations in a broader context additional East Asiatic and North American species of the same subgenus Fagus as well as two species of the subgenus Engleriana were included in our study. The morphological features exhibited in western Eurasiatic populations of Fagus show a westeast gradient that is characterised by strongly overlapping variability between geographical races. Fagus populations from Asia Minor exhibit an even higher variability that is also reflected in their genetic variability of nuclear rDNA internal transcribed spacer (ITS) sequences. The intraspecific genetic variability recorded here is in conflict with previous ITS studies in Fagus. The high amount of ITS polymorphism within Fagus from western Eurasia along with the clinal variation observed for morphological characters suggest the presence of only a single species, Fagus sylvatica L., in Europe and Asia Minor. Previously recognised taxa such as F. orientalis Lipsky and Fagus moesiaca (Malý) Czeczott should therefore be treated as synonyms of Fagus sylvatica. Although species belonging to the subgenus Engleriana were genetically distinct from species of the subgenus Fagus, relationships within the subgenus Fagus could not be clearly resolved. A reason for this could be the low rate of diversification in Fagus during the early phase of range expansion of the genus in the Oligocene period as indicated by the uniformity of leaf and cupule/nut fossils. This may account for the low overall ITS divergence and the high degree of polymorphism encountered in the subgenus Fagus and points to a late differentiation of western Eurasiatic and eastern Asiatic species. Area disruptions during the Pleistocene and the post-glacial recolonisation of western Europe appear to have caused the west-east gradient that is apparent in modern Fagus of western Eurasia but absent in Late Tertiary ancestors of Fagus sylvatica.

The reticulate origin of modern plane trees (Platanus, Platanaceae): A nuclear marker puzzle

by Guido Grimm

Authored by: Grimm, Denk

Hybridization plays a major role in speciation. However, hybridization and reticulate evolution in general are poorly... more Hybridization plays a major role in speciation. However, hybridization and reticulate evolution in general are poorly understood in tree species because genetic documentation is often missing. Analyses of biparentally inherited gene regions allow detection of reticulate signals. Multicopy and single-copy nuclear markers may show significant intraindividual variability
owing to reticulation processes. Naturally, such processes induce incompatible phylogenetic signal resulting in incongruent genealogies. Data from three nuclear markers, two multicopy nrDNA spacers, and the single-copy 2nd intron of the LEAFY gene, mirror ancient and recent horizontal gene flow in plane trees (Platanus). In addition to previously assembled data from the internal transcribed spacers (ITS) of the 35S ribosomal DNA, we found atypical 5S rDNA intergenic spacer sequences (5S-IGS) causing significant intra- and interindividual polymorphism, and a conspicuous LEAFY intron dimorphism. A detailed framework of reticulate molecular evolution of Platanus can be erected using splits graphs based on distances between cloned sequences or individuals, and competing topologies. Two hundred and sixty-one 5S-IGS sequences and LEAFY genotyping of 71 individuals via sequence analysis and PCR-RFLP support a previous ITS study (including pseudogenous and non-pseudogenous variants) suggesting that the modern North American taxa P. rzedowskii and P. occidentalis var. palmeri are the result of ancient hybridization. Platanus occidentalis var. palmeri requires taxonomic revision and is provisionally treated at species rank.

Molecular and phytosociological insight into postglacial relicts Lathyrus pannonicus and Oxytropis pilosa

by Guido Grimm

Authored by Schlee and co-workers
Proceedings (abstracts) of the conference "Phylogeography and Conservation of Postglacial Relicts" held in Luxemburg, 2007

[Extended abstract] [Extended abstract]

Genetic patterns in the Lathyrus pannonicus complex (Fabaceae) reflect ecological differentiation rather than biogeography and traditional subspecific division

by Guido Grimm

Authored by Schlee, Göker, Grimm, Hemleben

The endangered European relict species complex Lathyrus pannonicus shows distinct morphological variation, reflected... more The endangered European relict species complex Lathyrus pannonicus shows distinct morphological variation, reflected by the number of subspecies recognized, and complicated patterns of genetic variation. The traditionally recognized subspecies appear to possess different ecological preferences and disjunct distributions, particularly in the western range of the species. In this study, L. pannonicus was investigated by the correlation of distance matrices based on phytosociological, ecological, molecular and morphological data. Ecological characteristics of selected stands of L. pannonicus throughout Europe were assessed using ‘Ellenberg values’ of all the constituent taxa in phytosociological relevés. Genetic distances were calculated using recently developed methods to analyse high degrees of intra-individual nuclear-encoded internal transcribed spacer variability. We found that the remarkable genetic (and morphological) diversity in L. pannonicus could not be explained solely by the fragmentation of the distributional range. Instead, patterns of morphological and genetic differentiation were a reflection of the moisture regime in the sampled stands. Two major lineages could be identified: (1) a lineage adapted to dry conditions (Ellenberg indicator F-value ≤ 3.5) and (2) a lineage preferring moist conditions (F-value ≥ 4.5). Although both lineages occurred in close proximity in the Pannonian area, they appeared to be reproductively isolated in general. Further data are needed to determine whether these genetically and ecologically defined lineages, or ecospecies, within the L. pannonicus species complex can be formalized as (Linnaean) species or subspecies.

Ahern 2006 - Neandertal unique traits

by James Ahern

A new method for producing allohexaploid Brassica through unreduced gametes

by Annaliese Mason

Annaliese S. Mason, Guijun Yan, Wallace A. Cowling and Matthew N. Nelson; Euphytica (2011), Online first DOI: 10.1007/s10681-011-0537-4

We trialled a two-step method of producing allohexaploid Brassica with three genomes (A, B, and C) derived from... more We trialled a two-step method of producing allohexaploid Brassica with three genomes (A, B, and C) derived from pair-wise crossing among three allotetraploid Brassica species. In the first step, the three allotetraploid Brassica species (Brassica juncea, AjAjBjBj; Brassica napus, AnAnCnCn; and Brassica carinata, BcBcCcCc) were intercrossed in pairs to produce unbalanced trigenomic hybrids: AjAnBjCn, BjBcAjCc and CnCcAnBc. In the second step, these hybrids were crossed with the complementary allotetraploid parent, that is, AjAnBjCn × BcBcCcCc (B. carinata), BjBcAjCc × AnAnCnCn (B. napus) and CnCcAnBc × AjAjBjBj (B. juncea). We hypothesised that the unbalanced trigenomic hybrids would produce high levels of unreduced gametes with the same genome composition as the hybrid. These unreduced gametes would unite with reduced gametes from the complementary allotetraploids to form allohexaploid Brassica progeny (AjAnBcBjCcCn). From 112 s generation interspecific progeny, two progeny were shown by locus-specific simple sequence repeat markers to be near-allohexaploids derived from an unreduced gamete from CnCcAnBc and a reduced gamete from B. juncea (AjBj). One of these plants was highly self-fertile, had 50 chromosomes, and inherited patterns of marker alleles (AjAnBcBjCcCn) that were predicted from first division restitution at meiosis in the CnCcAnBc parent. The second near-allohexaploid had 60 chromosomes, was sterile, and inherited patterns of marker alleles that indicated second division restitution in the CnCcAnBc parent. Trigenomic hybrid Brassica produced by these methods will be valuable bridges to move alleles between allotetraploid species, and may contribute useful meiotic stability alleles to a future allohexaploid species.

Incipient sexual isolation in Laupala cerasina: females discriminate population-level divergence in acoustic characters

by Jaime Grace

Uncorrected proof, will appear in a special column of Current Zoology, guest edited by Maria Servedio, with theme "Sexual selection and speciation". Coauthored with my Ph.D. advisor, Kerry Shaw. I have just received the proofs and the paper will be published in the June issue, 2012

Sexual selection by female choice can shape the evolution of male traits within populations, since the most attractive... more Sexual selection by female choice can shape the evolution of male traits within populations, since the most attractive males experience an increase in fitness through elevated mating success. Speciation by sexual selection occurs when evolution in traits and preferences within populations causes differentiation among populations, such that females in alternative populations prefer sexual signals of their own population relative to others. Differentiated traits and preferences thereby play an active role in limiting gene flow between divergent populations. The effectiveness of differentiated preferences in maintaining differentiated male signals against the homogenizing effects of gene flow across populations will be limited by both the degree to which females can discriminate against non-local males, and the breeding values of traits and preferences. Populations of the Hawaiian cricket Laupala cerasina have diverged in pulse rate, a sexually selected male signal, and female acoustic preference for pulse rate. Gene flow between neighboring populations may be reduced if migrants from sexually diverged populations experience reduced mating success. We show that females discriminate among divergent songs characteristic of neighboring populations, that differences among populations in song and preference breed true in a common environment, and that mean preferences for each population closely match the mean pulse rates. Divergence in preference was observed only between populations that also differed in song. Along with a striking ability to discriminate slight differences in song, correlated evolution of song and preference within populations could be a mechanism that promotes assortative mating among populations, thereby reducing gene flow, and leading to speciation in Laupala.

Persistent predator–prey dynamics revealed by mass extinction

by Lauren Sallan

End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates

by Lauren Sallan

Heads or tails: staged diversification in vertebrate evolutionary radiations

by Lauren Sallan

Systematic Palaeobotany

by Fridgeir Grimsson

2011
Thomas Denk, Fridgeir Grimsson, Reinhard Zetter, Leifur A Simonarson
Springer
Chapter 3

A Brief Review of Palaeobotanical Research in Iceland

by Fridgeir Grimsson

2011
Thomas Denk, Fridgeir Grimsson, Reinhard Zetter, Leifur A Simonarson
Springer
Chapter 2

Combined LM and SEM study of the Middle Miocene (Sarmatian) palynoflora from the Lavanttal Basin: Part II. Pinophyta (Cupressaceae, Pinaceae and Sciadopityaceae)

by Fridgeir Grimsson

2011
Fridgeir Grimsson, Reinhard Zetter
Grana

Preliminary chromosome studies of some Nevada Test Site lizards

by William P. Hall

1965. Hall, W.P. Preliminary chromosome studies of some Nevada Test Site lizards. Paper given at the Annual Meeting of the American Society of Ichthyologists and Herpetologists, Lawrence, Kansas.

Among the approximately 60 species of the lizard genus Sceloporus, there is much karyotypic diversity, resulting... more Among the approximately 60 species of the lizard genus Sceloporus, there is much karyotypic diversity, resulting primarily from the fixation of "Robertsonian rearrangements" (centric fusions and fissions; Hsu and Mead, 1969; Jackson, 1971). Diploid (2n) chromosome numbers vary from 22 to 46 (Cole, 1970, 1971; Hall, 1973), a range exceeding that known for any other lizard genus. Because comparable variation has been detected in several groups of vertebrates, including other lizard genera (Gorman and Atkins, 1968; Matthey and van Brink, 1960) and rodents (review by Nadler, 1969), and in many invertebrates, evolutionists are becoming increasingly concerned with the role of karyotypic changes in animal speciation (White, 1969; Mayr, 1969, 1970). To investigate relationships between karyotypic diversification and speciation, Hall has undertaken a survey of chromosomal variation in Sceloporus and related genera, seeking particularly to identify intermediate evolutionary stages. Of 48 species of Sceloporus examined, all but one, the Mexican form S. grammicus, are karyotypically monomorphic, at least for Robertsonian mutations of the autosomes. An analysis of 1200 individuals of S. grammicus has revealed extensive chromosomal diversity at several levels of population structure, including the occurrence of rare individual variants, polymorphism, and the fixation of different Robertsonian modifications in parapatrically or allopatrically distributed populations. Chromosome numbers vary geographically from 2n = 31 to 2n = 46. The available data on karyotypic variation and geographic and ecologic distributions of populations suggest that the morphologically defined taxon S. grammicus (Smith, 1939; Smith and Laufe, 1945) actually represents several semispecies or cryptic species in early stages of differentiation. In the present study we have examined patterns of karyotypic and genic variation in a zone of contact between two karyotypically distinctive populations of grammicus to determine the extent of their genetic isolation. This research has implications for the systematic problem of defining species limits in the grammicus complex and contributes to an understanding of the evolutionary significance of parapatric hybridization.

Quantifying ecological, morphological, and genetic variation to delimit species in the coast horned lizard species complex (Phrynosoma)

by Carol Spencer

Defining Species: A Multi-Level Approach

by Tudor Baetu

forthcoming in Acta Biotheoretica DOI: 10.1007/s10441-011-9143-z

Different concepts define species at the pattern-level grouping of organisms into discrete clusters, the level of the... more Different concepts define species at the pattern-level grouping of organisms into discrete clusters, the level of the processes operating within and between populations leading to the formation and maintenance of these clusters, or the level of the inner-organismic genetic and molecular mechanisms that contribute to species cohesion or promote speciation. I argue that, unlike single level approaches, a multi-level framework takes into account the complex sequences of cause effect reinforcements leading to the formation and maintenance of various patterns, and allows for revisions and refinements of pattern-based characterizations in light of the gradual elucidation of the causes and mechanisms contributing to pattern formation and maintenance.

Major patterns and processes in biodiversity: taxonomic diversity on islands explained in terms of sympatric speciation

by Alexandra van der Geer

A biogeographic comment on: Wüster et al.(2005) Tracing an invasion: landbridges, refugia, and the phylogeography of the Neotropical rattlesnake (Serpentes: …

by William Gosling

Gosling, W.D. and Bush, M.B. (2005). A biogeographic comment on: Wüster, W. et al. (2005) Tracing an invasion: landbridges, refugia, and the phylogeography of the Neotropical rattlesnake (Serpentes: Viperidae: Crotalus durissus). Molecular Ecology, 14(11): 3615-3617.