Geology topics

Michael J. Blum

Publications and source records attributed to Michael J. Blum.

4 recordsLinked to original sources

USGS2016

Rapid movement and instability of an invasive hybrid swarm

Unstable hybrid swarms that arise following the introduction of non-native species can overwhelm native congeners, yet the stability of invasive hybrid swarms has not been well documented over time. Here we examine genetic variation and clinal stability across a recently formed hybrid swarm involving native blacktail shiner ( Cyprinella venusta ) and non-native red shiner ( C. lutrensis ) in the Upper Coosa River basin, which is widely considered to be a global hotspot of aquatic biodiversity. Examination of phenotypic, multilocus genotypic, and mitochondrial haplotype variability between 2005 and 2011 revealed that the proportion of hybrids has increased over time, with more than a third of all sampled individuals exhibiting admixture in the final year of sampling. Comparisons of clines over time indicated that the hybrid swarm has been rapidly progressing upstream, but at a declining and slower pace than rates estimated from historical collection records. Clinal comparisons also showed that the hybrid swarm has been expanding and contracting over time. Additionally, we documented the presence of red shiner and hybrids farther downstream than prior studies have detected, which suggests that congeners in the Coosa River basin, including all remaining populations of the threatened blue shiner ( Cyprinella caerulea) , are at greater risk than previously thought.

Alabama↗

USGS2015

Turbidity alters pre-mating social interactions between native and invasive stream fishes

Environmental degradation can result in the loss of aquatic biodiversity if impairment promotes hybridisation between non-native and native species. Although aquatic biological invasions involving hybridisation have been attributed to elevated water turbidity, the extent to which impaired clarity influences reproductive isolation among non-native and native species is poorly understood. We examined whether turbidity influences intraspecific and interspecific pre-mating social interactions between invasive red shiner ( Cyprinella lutrensis ) and native blacktail shiner ( Cyprinella venusta ) from the Upper Coosa River Basin (U.S.A.). We found that the number or duration of conspecific and heterospecific interactions increased under turbid conditions. Additionally, we found evidence indicating that native blacktail shiner females are especially likely to interact with invasive red shiner males due to species- and sex-specific responses to turbid conditions. These findings suggest that elevated turbidity can increase pre-mating social interactions between native and invasive species, which could result in greater hybridisation and promote the genetic assimilation of native species following species introductions. Thus, integrating knowledge of species behaviour into conservation and management planning can help deter the establishment and spread of invasive species.

Freshwater Biology↗

USGS2013

Geographic range and structure of cryptic genetic diversity among Pacific North American populations of the non-native amphipod Grandidierella japonica

Reconstructing the invasion history of aquatic invasive species can enhance understanding of invasion risks by recognizing areas most susceptible to invasion and forecasting future spread based on past patterns of population expansion. Here we reconstruct the invasion history of the Japanese amphipod Grandidierella japonica Stephensen 1938 combining information from historical collection data with molecular genetic data to better understand post-invasion range expansion and anthropogenic connectivity across the Pacific coast of North America. Compilation of collection data from bays and estuaries of the Pacific North American coast show many new localities have been colonized in the last two decades, moving outward from harbors and bays with high commercial traffic into smaller coastal locations dominated by local recreational traffic. DNA barcode sequence data for G. japonica reveals two distinct clades: one found in San Francisco Bay and sites to the north, and one also found in San Francisco Bay and sites to the south. The two clades differ by an average 7.28 % genetic distance, large enough to consider these invasive amphipods two separate species. Both northern and southern clades exhibit low levels of genetic diversity, suggesting a single introduction event for each. The presence of cryptic diversity within this invasive amphipod highlights the need for more extensive study of the invasive and native populations of aquatic invasive invertebrates to address questions of taxonomy, diversity, and invasion history.

California, Oregon, Washington↗

USGS2010

Reproductive isolation and the expansion of an invasive hybrid swarm

Biological invasions involving hybridization proceed according to prezygotic and postzygotic reproductive isolating mechanisms. Yet few comparisons of reproductive isolation have been carried out to understand how different mechanisms prevent or promote invasions involving hybridization. Here we present a study of prezygotic and postzygotic isolation between non-native red shiner ( Cyprinella lutrensis ) and native blacktail shiner ( C. venusta stigmatura ) from the Coosa River basin (USA) to better understand the formation and expansion of invasive hybrid swarms. We conducted spawning trials to measure mating preferences and raised broods from crosses to assay hybrid viability through early juvenile development. Females of both species were more responsive to conspecific mates, although blacktail shiner females responded more often to heterospecific mates than did red shiner females. Fecundity of red shiner females was also higher than blacktail shiner females. Heterospecific crosses resulted in lower fertilization and egg hatching rates, but we found no other evidence of inviability. Rather, we found comparatively low larval mortality of F1 hybrids, which is suggestive of heterosis. These findings support prior inferences of assortative mating from genetic descriptions of hybridization, and that the invasion in the Coosa River is likely proceeding due to interspecific competition and intrinsic hybrid viability.

Biological Invasions↗