Loss of genetic diversity in the North American mayfly Ephemerella invaria associated with deforestation of headwater streams

Abstract

Summary 1. Terrestrial dispersal by aquatic insects increases population connectivity in some stream species by allowing individuals to move outside the structure of the stream network. In addition, individual survival and reproductive success (as well as dispersal) are tightly linked to the quality of the terrestrial habitat. 2. In historically forested catchments, deforestation and altered land use have the potential to interfere with mayfly dispersal or mating behaviours by degrading the quality of the terrestrial matrix among headwater streams. We hypothesised that loss of tree cover in first‐order catchments would be associated with an increase in population substructure and a decrease in genetic diversity of mayfly populations. 3. To test this hypothesis, we investigated spatial patterns of genetic variation in the common mayfly Ephemerella invaria across a gradient of deforestation in the central piedmont region of eastern United States. Intraspecific genetic diversity and population substructure were estimated from data obtained using fluorescent amplified fragment length polymorphism (AFLP) markers. 4. We found that mayfly populations had low population substructure within headwater stream networks and that genetic diversity was strongly negatively correlated with mean deforestation of the first‐order catchments. The large‐scale pattern of population substructure followed a pattern of isolation by distance (IBD) in which genetic differentiation increases with geographical distance, but assignment tests placed a few individuals into populations 300 km away from the collection site. 5. Our results show that loss of genetic diversity in this widespread aquatic insect species is co‐occurring with deforestation of headwater streams. 6. Most arguments supporting protection of headwater streams in the United States have centred on the role of these streams as hydrological and biogeochemical conduits to downstream waters. Our work suggests that headwater stream land use, and specifically tree cover, may have a role in the maintenance of regional genetic diversity in some common aquatic insect species.

Small‐scale patterns of genetic variation in a headwater specialist mayfly: No influence of selective forest harvesting on diversity

“…AV2 would be sensitive to the potentially isolating effects of forest harvesting in headwater streams based on its adult flight stage and preference for good water quality (signal score of 8: Chessman 2003). Their results suggested there was no observable impact on diversity until the level of catchment clearing reached at least 40-50%, after which diversity was found to decrease with increasing percentage area of catchment clearing (Alexander et al 2011). However, we found no significant difference between selectively harvested and non-harvested sub-catchments for any of the diversity indices.…”

“…A study in northern Australia on the chironomid Echinocladius martini found natural habitat fragmentation as a result of extensive historical climatic fluctuations might have isolated historical populations, driving genetic divergence in allopatry (Krosch et al 2009). One other study showed that deforestation reduced genetic diversity in a mayfly population in eastern USA as a result of habitat loss, both instream and terrestrial, and through reduced dispersal of adults (Alexander et al 2011). One other study showed that deforestation reduced genetic diversity in a mayfly population in eastern USA as a result of habitat loss, both instream and terrestrial, and through reduced dispersal of adults (Alexander et al 2011).…”

“…clear-cutting), little is known about the potential effects of less intensive forms of timber harvest such as selective logging (single tree selection), which presumably have less negative effects on aquatic communities. The only study documenting these direct effects of logging on aquatic insect genetic diversity (Alexander et al 2011) found that a loss of genetic diversity of a mayfly population co-occurred with deforestation and degradation of headwater streams in historically forested headwater catchments in the USA. This disturbance has been considered to produce little effect on forest structure, composition and dynamics (Deckker & de Graaf 2003), thus maintaining natural microclimatic conditions within the forest.…”

“…We know that forest harvesting can decrease the dispersal of mayflies, thereby reducing population connectivity and genetic diversity (Alexander et al 2011). We hypothesized that (i) patterns of mitochondrial DNA (mtDNA) variation in a Leptophlebiidae mayfly show a pattern of structuring that reflects widespread dispersal along the stream network and across catchments, and (ii) genetic diversity will be lower in partially deforested sub-catchments compared to forested sub-catchments because a barrier to dispersal could effectively isolate mayfly populations within separate headwater streams.…”

Human effects on ecological connectivity in aquatic ecosystems: Integrating scientific approaches to support management and mitigation

“…Other disturbances, such as fire (Brown et al 2001) and deforestation (Alexander et al 2011), occur over areas of the landscape that are not constrained by the dendritic river network. Because the movements of obligate aquatic organisms are constrained to the river channel, these terrestrially based disturbances can lead to a mismatch 350 between the geometry of dispersal pathways and the geometry of landscape disturbances (Fagan 2002).…”