The rise and fall of proboscidean ecological diversity.

Proboscideans were keystone Cenozoic megaherbivores and present a highly relevant case study to frame the timing and magnitude of recent megafauna extinctions against long-term macroevolutionary patterns. By surveying the entire proboscidean fossil history using model-based approaches, we show that the dramatic Miocene explosion of proboscidean functional diversity was triggered by their biogeographical expansion beyond Africa. Ecomorphological innovations drove niche differentiation; communities that accommodated several disparate proboscidean species in sympatry became commonplace. The first burst of extinctions took place in the late Miocene, approximately 7 million years ago (Ma). Importantly, this and subsequent extinction trends showed high ecomorphological selectivity and went hand in hand with palaeoclimate dynamics. The global extirpation of proboscideans began escalating from 3 Ma with further extinctions in Eurasia and then a dramatic increase in African extinctions at 2.4 Ma. Overhunting by humans may have served as a final double jeopardy in the late Pleistocene after climate-triggered extinction trends that began long before hominins evolved suitable hunting capabilities.

Mitochondrial genomes reveal the extinct Hippidion as an outgroup to all living equids.

Hippidions were equids with very distinctive anatomical features. They lived in South America 2.5 million years ago (Ma) until their extinction approximately 10 000 years ago. The evolutionary origin of the three known Hippidion morphospecies is still disputed. Based on palaeontological data, Hippidion could have diverged from the lineage leading to modern equids before 10 Ma. In contrast, a much later divergence date, with Hippidion nesting within modern equids, was indicated by partial ancient mitochondrial DNA sequences. Here, we characterized eight Hippidion complete mitochondrial genomes at 3.4-386.3-fold coverage using target-enrichment capture and next-generation sequencing. Our dataset reveals that the two morphospecies sequenced (H. saldiasi and H. principale) formed a monophyletic clade, basal to extant and extinct Equus lineages. This contrasts with previous genetic analyses and supports Hippidion as a distinct genus, in agreement with palaeontological models. We date the Hippidion split from Equus at 5.6-6.5 Ma, suggesting an early divergence in North America prior to the colonization of South America, after the formation of the Panamanian Isthmus 3.5 Ma and the Great American Biotic Interchange.

Global evolution of Equidae and Gomphotheriidae from South America.

The contemporary South American mammalian communities were determined by the emergence of the Isthmus of Panama and by the profound climatic oscillations during the Pleistocene. Horses and gomphotheres were 2 very conspicuous groups of immigrant mammals from North America that arrived in South America during the Pleistocene. The present study compiles updated data on the phylogeny, systematics and ecology of both groups in South America. The horses in South America are represented by 2 genera, Hippidion and Equus, as are the gomphotheres, represented by Cuvieronius and Stegomastodon. Both genera of horses include small (Hippidion devillei, H. saldiasi, E. andium and E. insulatus) and large forms (Equus neogeus and H. principale), which dispersed into South America using 2 different routes. The possible model for this dispersion indicates that the small forms used the Andes corridor, while larger horses dispersed through the eastern route and through some coastal areas. In the case of gomphotheres, Cuvieronius and Stegomastodon reached South America in 2 independent dispersal events, and Cuvieronius dispersed across the Andean corridor, while large Stegomastodon spread along the eastern route. Horses and gomphotheres present values of δ(13) C from woodlands to C4 grasslands. Hippidion present lower values of δ(13) C than Equus in the late Pleistocene, whereas the gomphotheres diverge from value of δ(18) O, reflecting that Cuvieronius inhabited the Andean corridor and Stegomastodon dispersed through eastern plains. The gomphothere and horse species recorded in South America became extinct around the time that humans arrived.

Ancient feeding ecology inferred from stable isotopic evidence from fossil horses in South America over the past 3 Ma.

BACKGROUND: Stable isotope ratios (13C/12C and 18O/16O) in fossil teeth and bone provide key archives for understanding the ecology of extinct horses during the Plio-Pleistocene in South America; however, what happened in areas of sympatry between Equus (Amerhippus) and Hippidion is less understood. RESULTS: Here, we use stable carbon and oxygen isotopes preserved in 67 fossil tooth and bone samples for seven species of horses from 25 different localities to document the magnitude of the dietary shifts of horses and ancient floral change during the Plio-Pleistocene. Dietary reconstructions inferred from stable isotopes of both genera of horses present in South America document dietary separation and environmental changes in ancient ecosystems, including C3/C4 transitions. Stable isotope data demonstrate changes in C4 grass consumption, inter-species dietary partitioning and variation in isotopic niche breadth of mixed feeders with latitudinal gradient. CONCLUSIONS: The data for Hippidion indicate a preference varying from C3 plants to mixed C3-C4 plants in their diet. Equus (Amerhippus) shows three different patterns of dietary partitioning Equus (A.) neogeus from the province of Buenos Aires indicate a preference for C3 plants in the diet. Equus (A.) andium from Ecuador and Equus (A.) insulatus from Bolivia show a preference for to a diet of mixed C3-C4 plants, while Equus (A.) santaeelenae from La Carolina (sea level of Ecuador) and Brazil are mostly C4 feeders. These results confirm that ancient feeding ecology cannot always be inferred from dental morphology. While the carbon isotope composition of horses skeletal material decreased as latitude increased, we found evidence of boundary between a mixed C3/C4 diet signal and a pure C4 signal around 32° S and a change from a mixed diet signal to an exclusively C3 signal around 35°S.We found that the horses living at high altitudes and at low to middle latitude still have a C4 component in their diet, except the specimens from 4000 m, which have a pure C3 diet. The change in altitudinal vegetation gradients during the Pleistocene is one of several possibilities to explain the C4 dietary component in horses living at high altitudes. Other alternative explanations imply that the horses fed partially at lower altitudes.

Revising the recent evolutionary history of equids using ancient DNA.

The rich fossil record of the family Equidae (Mammalia: Perissodactyla) over the past 55 MY has made it an icon for the patterns and processes of macroevolution. Despite this, many aspects of equid phylogenetic relationships and taxonomy remain unresolved. Recent genetic analyses of extinct equids have revealed unexpected evolutionary patterns and a need for major revisions at the generic, subgeneric, and species levels. To investigate this issue we examine 35 ancient equid specimens from four geographic regions (South America, Europe, Southwest Asia, and South Africa), of which 22 delivered 87-688 bp of reproducible aDNA mitochondrial sequence. Phylogenetic analyses support a major revision of the recent evolutionary history of equids and reveal two new species, a South American hippidion and a descendant of a basal lineage potentially related to Middle Pleistocene equids. Sequences from specimens assigned to the giant extinct Cape zebra, Equus capensis, formed a separate clade within the modern plain zebra species, a phenotypicically plastic group that also included the extinct quagga. In addition, we revise the currently recognized extinction times for two hemione-related equid groups. However, it is apparent that the current dataset cannot solve all of the taxonomic and phylogenetic questions relevant to the evolution of Equus. In light of these findings, we propose a rapid DNA barcoding approach to evaluate the taxonomic status of the many Late Pleistocene fossil Equidae species that have been described from purely morphological analyses.

Lolium rigidum, a pool of resistance mechanisms to ACCase inhibitor herbicides.

Three diclofop-methyl (DM) resistant biotypes of Lolium rigidum (R1, R2, and R3) were found in different winter wheat fields in Spain, continuously treated with DM, DM + chlortoluron, or DM + isoproturon. Herbicide rates that inhibited shoot growth by 50% (ED50) were determined for DM. There were found that the different biotypes exhibited different ranges of resistance to this herbicide; the resistant factors were 7.2, 13, and 36.6, respectively. DM absorption, metabolism, and effects on ACCase isoforms were examined in these biotypes of L. rigidum. The most highly resistant, biotype R3, contained an altered isoform of ACCase. In biotype R2, which exhibited a medium level of resistance, there was an increased rate of oxidation of the aryl ring of diclofop, a reaction most likely catalyzed by a cytochrome P450 enzyme. In the other biotype, R1, DM penetration was significantly less than that observed in the resistant (R2 and R3) and susceptible (S) biotypes. Analysis of the leaf cuticle surface by scanning electron microscopy showed a greater epicuticular wax density in the leaf cuticles of biotype R1 than in the other biotypes.