Lizards as model organisms for linking phylogeographic and speciation studies

Lizards have been model organisms for ecological and evolutionary studies from individual to community levels at multiple spatial and temporal scales. Here we highlight lizards as models for phylogeographic studies, review the published population genetics/phylogeography literature to summarize general patterns and trends and describe some studies that have contributed to conceptual advances. Our review includes 426 references and 452 case studies: this literature reflects a general trend of exponential growth associated with the theoretical and empirical expansions of the discipline. We describe recent lizard studies that have contributed to advances in understanding of several aspects of phylogeography, emphasize some linkages between phylogeography and speciation and suggest ways to expand phylogeographic studies to test alternative pattern‐based modes of speciation. Allopatric speciation patterns can be tested by phylogeographic approaches if these are designed to discriminate among four alternatives based on the role of selection in driving divergence between populations, including: (i) passive divergence by genetic drift; (ii) adaptive divergence by natural selection (niche conservatism or ecological speciation); and (iii) socially‐mediated speciation. Here we propose an expanded approach to compare patterns of variation in phylogeographic data sets that, when coupled with morphological and environmental data, can be used to to discriminate among these alternative speciation patterns. [Correction made after online publication (28/07/2010): (minor deletion in the last line of the abstract)].     

Defoliation alters the relative contributions of recent and non-recent assimilate to root exudation from Festuca rubra

The deposition of organic compounds from plant roots is a key determinant of rhizosphere microbial activity and community structure. Consequently, C-flow from roots to soil is an important process in coupling plant and microbial productivity, via impacts on microbial nutrient cycling in soil. Experimentally, isotopic tracers (¹³C or ¹⁴C) are used to track C inputs to soil and microbial communities. However, in many such studies the relationship between labelled C-flows and total C-flows are not established, limiting the interpretative value of the results. In this study, we applied steady-state near natural abundance ¹³CO₂ labelling to determine the impact of partial defoliation of Festuca rubra on root exudation. This approach in axenic culture facilitated determination of the contribution of pre- and post-defoliation assimilates both to root C-flow and plant tissues. The results demonstrated that total root exudation was increased in the two days following defoliation. This was concurrent with reduced net CO₂ assimilation and reduced allocation of post-defoliation assimilates below-ground and to active root meristems. Through determination of the δ¹³C of root exudates, it was established that the source of the increased root exudation was pre-defoliation assimilate. However, this response was transient, with reduced deposition of pre- and post-defoliation assimilates from roots during the period 2–4 d following defoliation. The results highlight the limitations of pulse-labelling approaches as a means of quantifying impacts of treatments on root exudation, particularly where the treatment is likely to affect plant C-partitioning or the balance between deposition to, and re-mobilization from, C-storage pools.     

Interspecific competition between mice: A reciprocal field manipulation experiment

Previous studies have demonstrated a species replacement sequence in disturbed forest and heathland, with the native New Holland mouse (Pseudomys novaehollandiae) replacing the introduced house mouse (Mus musculus) in the earliest part of the succession. The replacement appeared to be competitive displacement and this has been confirmed by controlled experimental removal of P. novaehollandiae from field sites, which produced significant increases in the abundance and habitat use of Mus musculus. This paper reports the results of the controlled reciprocal manipulation experiment in the field. A pulsed addition of M. musculus to three treatment plots produced significant reductions in the abundance and habitat use of P. novaehollandiae, when compared with control plots with no addition of M. musculus. This effect was observed only at high M. musculus densities, and the return to the control conditions within 3 months of the pulsed addition is consistent with asymmetric interspecific competition from competitively superior P. novaehollandiae. The importance of considering the regional abundance of M. musculus in relation to its competitive ability is stressed, as at high densities M. musculus is able to create its own ecological space contrary to its more usual competitively submissive status.     

Strategies in Neuroendocrine Neurophysiology

SYNOPSIS. Hormonal effects on selected indicators of neuralactivity are reviewed with reference to neuroendocrine mechanisms.The nature of brain recordings and their advantages and disadvantagesin neuroendocrine applications are discussed. The problems oflocalization of neuroendocrine mechanisms in place and timeare presented, with indications of which processes may be bestsuited to neurophysiological analysis.     

Palaeozoic tropical rainforests and their effect on global climates: is the past the key to the present?

Wetland forests, known as coal forests, extended over large areas of the palaeotropics during the Late Carboniferous and the Permian Periods. They were initiated during the Serpukhovian Age as a response to lowering sea levels having exposed large areas of continental shelf. They expanded dramatically during the late Bashkirian Age, but then contracted by over one‐half during the Kasimovian Age. The estimated loss of carbon sink probably resulted in an annual increase in atmospheric CO₂ of about 2–5 ppm, and coincided with clear evidence of global warming in both the northern and southern high latitudes. A return to cooler conditions in very Early Permian times coincided with an expansion of the palaeotropical coal forests in the Far East, but this was short‐lived and most of the rest of the Permian was a time of global warming. The Palaeozoic evidence clearly confirms that there is a correlation between levels of atmospheric CO₂ and global climates. However, care must be taken in extrapolating this evidence to the present‐day tropical forests, which do not act as a comparable unsaturated carbon sink.     

Variations in attack behaviours between Glossina palpalis gambiensis and G. tachinoides in a gallery forest suggest host specificity

Tsetse flies Glossina palpalis gambiensis and G. tachinoides are among the major vectors of sleeping sickness (Human African Trypanosomiasis‐HAT) and nagana (African Animal Trypanosomiasis – AAT) in West Africa. Both riparian species occur sympatrically in gallery forests of south west Burkina Faso, but little is known of their interspecies relationships although different authors think there may be some competition between them. The aim of this study was to check if sympatric species have different strategies when approaching a host. A man placed in a sticky cube (1 m × 1 m × 1 m) and a sticky black‐blue‐black target (1 m × 1 m) were used to capture tsetse along the Comoe river banks in a Latin Square design. The number and the height at which tsetse were caught by each capture method were recorded according to species and sex. Glossina p. gambiensis was more attracted to human bait than to the target, but both species were captured at a significantly higher height on the target compared with the human bait (P < 0.05). No significant difference in heights was found between G. tachinoides and G. p. gambiensis captured on targets (33 and 35 cm, respectively, P > 0.05). However, catches on human bait showed a significant difference in height between G. tachinoides and G. p. gambiensis (22.5 and 30.6 cm, respectively, P < 0.001). This study showed that these sympatric species had different attack behaviours to humans, which is not the case with the target. The implications of these findings are discussed.