On the geographic variability of a freshwater crustacean Polyphemus pediculus (Cladocera, Onychopoda)

Author

Butorina, Lyudmila G.

Specimens of Polyphemus pediculus (Linnaeus, 1761) from a shallow-water Yaroslavllocal population and a deep-water Michigan population at depths of 1.2, 9.3 and 23.6 m were compared by using nine quantitative and 12 meristic features. Experimental data were treated statistically by employing the methods of variance and multivariate analyses. The degree of reliability of morphometric differences between individuals was assessed by ratios of their sizes, coefficients of variation, ranges of variation, mean levels of variability and statistical differences of data by principal components. Geographic variability of morphometric features of P. pediculus is clearly expressed, but unstable. The variability magnitude and range vary depending on the geographic latitude, ecological conditions of habitation, crustacean age and sex, with differences evident with respect to certain quantitative and meristic features. The mean level of variability of P. pediculus quantitative features is approximately similar in the Yaros1av110ca1 population and in the Michigan population at a l.2-m depth (Cv = 22-23 %). At the depths of 9.3 and 23.6 m in Lake Michigan, the variability is lower by a factor of 1.5 and 2.7, respectively. The range of quantitative feature variability in the deep-water population (10.7 to 44.4 %) is wider, especially at the depth of 1.2 m, compared with the shallow-water population (9.5 %). In both populations, the quantitative features are most variable in parthenogenetic females. The mean level of P. pediculus meristic feature variability in the deep-water population (6.1 %) is 1.5-fo1d lower, and the range of variability is 1.7-fo1dwider, compared with the shallow-water population. The meristic features are most variable in immature specimens from the deep-water population (12.4 %), and in heterosexual individuals (9.4 %) from the shallow-water population. The level of geographic variability of morphometric features depends on the ecological conditions of existence of the local populations. Three ecological races, which differ reliably from each other, are distinguished in the deep-water Michigan population. The size of the crustacean body, antennae, caudal segment, the eye diameter, the length and the number of setae on the third segments of endopodites of limbs of I – III pairs are the principal discriminators of the species. Morphometric differences of the studied local populations indicate a considerable geographic variability of the species and a continuously proceeding gradual sympatric speciation.

Relative importance of environmental variables for the distribution of the invasive marsh species Spartina alterniflora across different spatial scales

Authors

Huiyu Liu, Haibo Gong, Xiangzhen Qi, Yufeng Li and Zhenshan Lin

The relative importance of environmental variables for Spartina alterniflora distribution was investigated across different spatial scales using maximum entropy modelling (MaxEnt), a species distribution modelling technique. The results showed that elevation was the most important predictor for species presence at each scale. Mean diurnal temperature range and isothermality were the second most important predictors at national and regional scales respectively. Soil drainage class, pH and organic carbon were important on the northern Chinese coast. The importance of climatic variable type was highest at global and national scales and declined as the scale decreased. The importance of soil variable type was lower at coarser scales, but varied greatly at finer scales. The relationships between environmental variables and species presence changed as the variables’ ranges changed across different scales. Climatic and soil variables were substantially affected by interactions among variables, which changed their relationships with species presence and relative importance. The modelled suitable area on the Chinese coast decreased from 54.16 to 12.64% limited by elevation from the global to national scale, and decreased to 8.04% limited by soil drainage, pH and organic carbon from the national to regional scale. The findings of the present study emphasise the importance of spatial scale for understanding relationships between environmental variables and the presence of S. alterniflora.

Predicting habitat suitability for eleven imperiled fluvial freshwater mussels

Authors

Wesley M. Daniel, Arthur R. Cooper, Peter J. Badra, Dana M. Infante

Understanding patterns in freshwater mussel distributions and habitat use, particularly for imperiled species, is critical for their conservation. To aid in management of imperiled mussels, and to demonstrate the utility using both landscape-based and biotic predictors in assessing species habitat suitability, we modeled 11 imperiled mussels in rivers of Michigan, USA. Models were developed with MaxEnt using a combination of host fish richness, natural abiotic reach variables, and landscape-based natural and anthropogenic variables. Because potential host fishes are important biological determinants of mussel distributions, fluvial host fish distributions (n = 37) were modeled and integrated as a predictor in mussel models. Key predictors determining habitat suitability for mussels included host fish richness, a strong positive predictor for 8 of 11 mussel species, stream discharge, urban land use, and upstream dam density. Models predicted 853 to 10,138 stream km of suitable habitat (1.1 to 13.6% of the state’s stream length) for the 11 mussel species, with 54 to 1,382 km (0.1 to 1.8%) being considered highly suitable habitat. Mapping of suitable habitats identified streams with available habitat for multiple listed species, allowing for more informed decisions in conservation planning and management of Michigan’s listed freshwater mussels and their fish hosts.

Re-assessing the origins of the invasive mussel Mytilus galloprovincialis in southern Africa

Authors

G. I. Zardi, C. D. McQuaid, R. Jacinto, C. R. Lourenço, E. A. Serrão and K. R. Nicastro

Retracing the origins of invasive species is a first critical step in identifying potential mechanisms of introduction, implementation of management strategies and forecasting the spread of the invader. Mytilus galloprovincialis is an intertidal mussel that is widely distributed in many temperate and subtropical regions. It is invasive worldwide and the most successful invasive marine species in southern Africa. Previous studies have examined genetic relationships between a few South African populations from the south-western coast and other worldwide populations, presenting evidence of a north-eastern Atlantic origin of the invasion. Here, a combination of nuclear (Me15/16 PCR-based) and mitochondrial (16S restriction fragment-length polymorphism; 16S RFLP) DNA assays was applied to infer the origin of this strong invader across its entire southern African distribution (South Africa and Namibia). The 16S RFLP confirmed the northern hemisphere as being the likely sole source of invasion. Additionally, the frequencies of haplotypes at the 16S marker and alleles at the Me15/16 locus point to north-eastern Atlantic shores as the most likely origin throughout the Namibian and South African distribution of the species.