Tracing the origins of widespread highland species: a case of Neogene diversification across the Mexican sierras in an endemic lizard

The evolutionary history of the Mexican sierras has been shaped by various geological and climatic events over the past several million years. The relative impacts of these historical events on diversification in highland taxa, however, remain largely uncertain owing to a paucity of studies on broadly‐distributed montane species. We investigated the origins of genetic diversification in widely‐distributed endemic alligator lizards in the genus Barisia to help develop a better understanding of the complex processes structuring biological diversity in the Mexican highlands. We estimated lineage divergence dates and the diversification rate from mitochondrial DNA sequences, and combined divergence dates with reconstructions of ancestral geographical ranges to track lineage diversification across geography through time. Based on our results, we inferred ten geographically structured, well supported mitochondrial lineages within Barisia. Diversification of a widely‐distributed ancestor appears tied to the formation of the Trans‐Mexican Volcanic Belt across central Mexico during the Miocene and Pliocene. The formation of filter barriers such as major river drainages may have later subdivided lineages. The results of the present study provide additional support for the increasing number of studies that suggest Neogene events heavily impacted genetic diversification in widespread montane taxa. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 382–394.     

Evaluation of offspring size–number invariants in 12 species of lizard

The optimal division of resources into offspring size vs. number is one of the classic problems in life‐history evolution. Importantly, models that take into account the discrete nature of resource division at low clutch sizes suggest that the variance in offspring size should decline with increasing clutch size according to an invariant relationship. We tested this prediction in 12 species of lizard with small clutch sizes. Contrary to expectations, not all species showed a negative relationship between variance in offspring size and clutch size, and the pattern significantly deviated from quantitative predictions in five of the 12 species. We suggest that the main limitation of current size–number models for small clutch sizes is that they rely on assumptions of hierarchical allocation strategies with independence between allocation decisions. Indeed, selection may favour alternative mechanisms of reproductive allocation that avoid suboptimal allocation imposed by the indivisible fraction at low clutch sizes.     

Isolation and characterisation of microsatellite markers for the Australian monitor lizard,Varanus acanthurus (Squamata: Varanidae) and their utility in other selected varanid species

There have been no molecular genetic examinations of mating systems in the Australian varanid lizards (genus Varanus) despite their high species diversity, the abundance of some species and difficulties with direct observation of behaviourally cryptic species in the field. We developed 10 polymorphic microsatellite loci and assessed their utility in a range of varanid species. Observed heterozygosities in the three species assessed ranged from 30% to 100%. These loci should be useful for investigation of population structure, gene flow and mating systems in Varanus acanthurus, V. baritji and V. tristis and may also be of use in other varanid species.     

How specialized is the plant–pollinator association between Eucalyptus globulus ssp. globulus and the swift parrot Lathamus discolor?

Abstract The swift parrot Lathamus discolor (Shaw) (Psittacidae) evolved from granivorous ancestors to become a specialized flower‐feeder in a monotypic genus. Its reproduction is dependent largely on flowers of Eucalyptus globulus Labill. ssp. globulus (Myrtaceae), the birds migrating to breed within the natural distribution of this tree. This paper investigates the extent to which this dependence of L. discolor on E. globulus is mirrored by dependence of the tree on the bird. It was found that L. discolor carried significantly more eucalypt pollen within 22 mm of its bill tip than did the New Holland honeyeater, Phylidonyris novaehollandiae (Latham) (Meliphagidae), and that pollen was concentrated on the regions of the head of L. discolor that consistently contact stigmas. Larger pollen loads on L. discolor can be attributed to it consuming both pollen and nectar, while honeyeaters take nectar only. The short thick bill of L. discolor necessitates regular stigmatic contact while the long slender bills of honeyeaters are unlikely to contact stigmas as often in these bowl‐shaped flowers. These factors suggest that L. discolor has a greater capacity to deposit pollen on stigmas of E. globulus than do honeyeaters. However, the characteristics of L. discolor that make it such an effective pollinator of E. globulus are also exhibited by a lorikeet (Psittacidae) that feeds on flowers of E. globulus. The association between E. globulus and L. discolor is therefore only moderately specialized because the flowers are also adapted to the more recently associated lorikeet and are almost certainly also pollinated by honeyeaters.     

Greater Sage-Grouse Winter Habitat Selection and Energy Development

Abstract Recent energy development has resulted in rapid and large-scale changes to western shrub-steppe ecosystems without a complete understanding of its potential impacts on wildlife populations. We modeled winter habitat use by female greater sage-grouse (Centrocercus urophasianus) in the Powder River Basin (PRB) of Wyoming and Montana, USA, to 1) identify landscape features that influenced sage-grouse habitat selection, 2) assess the scale at which selection occurred, 3) spatially depict winter habitat quality in a Geographic Information System, and 4) assess the effect of coal-bed natural gas (CBNG) development on winter habitat selection. We developed a model of winter habitat selection based on 435 aerial relocations of 200 radiomarked female sage-grouse obtained during the winters of 2005 and 2006. Percent sagebrush (Artemisia spp.) cover on the landscape was an important predictor of use by sage-grouse in winter. The strength of habitat selection between sage-grouse and sagebrush was strongest at a 4-km² scale. Sage-grouse avoided coniferous habitats at a 0.65-km² scale and riparian areas at a 4-km² scale. A roughness index showed that sage-grouse selected gentle topography in winter. After controlling for vegetation and topography, the addition of a variable that quantified the density of CBNG wells within 4 km² improved model fit by 6.66 Akaike's Information Criterion points (Akaike wt = 0.965). The odds ratio for each additional well in a 4-km² area (0.877; 95% CI = 0.834- 0.923) indicated that sage-grouse avoid CBNG development in otherwise suitable winter habitat. Sage-grouse were 1.3 times more likely to occupy sagebrush habitats that lacked CBNG wells within a 4-km² area, compared to those that had the maximum density of 12.3 wells per 4 km² allowed on federal lands. We validated the model with 74 locations from 74 radiomarked individuals obtained during the winters of 2004 and 2007. This winter habitat model based on vegetation, topography, and CBNG avoidance was highly predictive (validation R² = 0.984). Our spatially explicit model can be used to identify areas that provide the best remaining habitat for wintering sage-grouse in the PRB to mitigate impacts of energy development.     

Predicting leaf wax n‐alkane 2H/1H ratios: controlled water source and humidity experiments with hydroponically grown trees confirm predictions of Craig–Gordon model

The extent to which both water source and atmospheric humidity affect δ²H values of terrestrial plant leaf waxes will affect the interpretations of δ²H variation of leaf waxes as a proxy for hydrological conditions. To elucidate the effects of these parameters, we conducted a long‐term experiment in which we grew two tree species, Populus fremontii and Betula occidentalis, hydroponically under combinations of six isotopically distinct waters and two different atmospheric humidities. We observed that leaf n‐alkane δ²H values of both species were linearly related to source water δ²H values, but with slope differences associated with differing humidities. When a modified version of the Craig–Gordon model incorporating plant factors was used to predict the δ²H values of leaf water, all modelled leaf water values fit the same linear relationship with n‐alkane δ²H values. These observations suggested a relatively constant biosynthetic fractionation factor between leaf water and n‐alkanes. However, our calculations indicated a small difference in the biosynthetic fractionation factor between the two species, consistent with small differences calculated for species in other studies. At present, it remains unclear if these apparent interspecies differences in biosynthetic fractionation reflect species‐specific biochemistry or a common biosynthetic fractionation factor with insufficient model parameterization.     

Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus.