Ecological niche differentiation of polyploidization is not supported by environmental differences among species in a cosmopolitan grass genus

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PREMISE OF THE STUDY

Polyploidization frequently results in the creation of new plant species, the establishment of which is thought to often be facilitated by ecological niche differentiation from the diploid species. We tested this hypothesis using the cosmopolitan grass genus Phalaris (Poaceae), consisting of 19 species that range from diploid to tetraploid to hexaploid. Specifically, we tested whether (1) polyploids occupy more extreme environments and/or (2) have broader niche breadths and/or (3) whether the polyploid species' distributions indicate a niche shift from diploid species.•

METHODS

We employed a bootstrapping approach using distribution data for each species and eight environmental variables to investigate differences between species in the means, extremes, and breadths of each environmental variable. We used a kernel smoothing technique to quantify niche overlap between species.•

KEY RESULTS

Although we found some support for the three hypotheses for a few diploid-polyploid pairs and for specific environmental variables, none of these hypotheses were generally supported.•

CONCLUSIONS

Our results suggest that these commonly held hypotheses about the effects of polyploidization on ecological distributions are not universally applicable. Correlative biogeographic studies like ours provide a necessary first step for suggesting specific hypotheses that require experimental verification. A combination of genetic, physiological, and ecological studies will be required to achieve a better understanding of the role of polyploidization in niche evolution.

Chronic phalaris toxicity in eastern grey kangaroos (Macropus giganteus)

CASE REPORT

Seven eastern grey kangaroos (Macropus giganteus) grazing pastures including Phalaris spp. in Victoria showed neurological deficits characterised by ataxia, head tremors and collapse. Gross examination of the brains and spinal cords of affected kangaroos showed a greenish discolouration in several regions of the grey matter. Histologically, intracytoplasmic accumulation of pigment granules was detected in the neurons, most prominently in the thalamus, brainstem and ventral horns of the spinal cord. Pigment granules were positive to stains used for identification of melanin, including Fontana-Masson stain and Schmorl's reaction.

CONCLUSION

The combination of clinical signs and obvious neuronal pigmentation is consistent with chronic Phalaris spp. toxicity, a condition well documented in domestic ruminants.