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Aquatic Insects in Eastern Australia: A Window on Ecology and Evolution of Dispersal in Streams.

Hughes JM, Huey JA, McLean AJ, Baggiano O - Insects (2011)

Bottom Line: Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species.In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera.We conclude with a number of suggestions for further work.

View Article: PubMed Central - PubMed

Affiliation: Australian Rivers Institute and Griffith School of Environment, Griffith University, Nathan QLD 4111, Australia. jane.hughes@griffith.edu.au.

ABSTRACT
Studies of connectivity of natural populations are often conducted at different timescales. Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species. In contrast, studies conducted at historical timescales are usually more focused on evolutionary or biogeographic questions. In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera. We conclude that: (1) For both groups, the major mechanism of dispersal is by adult flight, with larval drift playing a very minor role and with unusual patterns of genetic structure at fine scales explained by the "patchy recruitment hypothesis"; (2) There is some evidence presented to suggest that at slightly larger spatial scales (~100 km) caddisflies may be slightly more connected than mayflies; (3) Examinations of three species at historical timescales showed that, in southeast Queensland Australia, despite there being no significant glaciation during the Pleistocene, there are clear impacts of Pleistocene climate changes on their genetic structure; and (4) The use of mitochondrial DNA sequence data has uncovered a number of cryptic species complexes in both trichopterans and ephemeropterans. We conclude with a number of suggestions for further work.

No MeSH data available.


Related in: MedlinePlus

Predictions for population genetic variation under two contrasting demographic models; the Stream Hierarchy Model and the Patchy Recruitment Model (A–C); (D) Shows different interpretations of deviations from Hardy-Weinberg Equilibrium. Red squares indicate significant deviations.
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f1-insects-02-00447: Predictions for population genetic variation under two contrasting demographic models; the Stream Hierarchy Model and the Patchy Recruitment Model (A–C); (D) Shows different interpretations of deviations from Hardy-Weinberg Equilibrium. Red squares indicate significant deviations.

Mentions: By designing sampling programs that included sites from both within the same stream, from different streams in the same subcatchments and from across catchment boundaries, it was possible to test these hypotheses. The idea was that if larval drift was the major mechanism of dispersal, then genetic variation should reflect the stream hierarchy, in other words, should fit the stream hierarchy model [15]. Samples from the same streams should be more similar than those from different subcatchments and those from different catchments should be greater again (Figure 1). Alternatively, if adult flight is the major mechanism of dispersal, then genetic differences between sites would reflect the straight line distance between them. An initial study using a freshwater shrimp that is limited to the stream network demonstrated that the stream hierarchy model was adhered to; with the greatest genetic differentiation between two catchments, with differentiation decreasing between sub-catchments and further between streams within sub-catchments and pools within streams [16]. The reverse effect was shown for three aquatic insect species: Bungona narilla, Tasiagma ciliata and Rheumatometra sp., which each showed the most differentiation between pools within a stream and the least across catchment boundaries [1,17,18]. Clearly, genetic variation in these species did not fit the stream hierarchy model. While this was assumed to imply that adult flight was the major dispersal mechanism, the result of large significant differences between pools within streams was unexpected. Further observations of the genetic data indicated that the differences were not consistent among genetic marker loci (allozymes) and that there were numerous samples that did not fit predictions of Hardy-Weinberg Equilibrium (HWE). These deviations did not occur consistently at particular sites or particular loci. These findings led to the suggestion that the results could result from the fact that pools did not contain a representative sample of the genetic diversity because they represented the offspring of a limited number of females and that larvae did not move much within the stream. The small number of families in each pool would explain both the deviations from Hardy-Weinberg predictions and apparent differences between streams. This idea was labeled the “patchy recruitment hypothesis” (PRH) [1].


Aquatic Insects in Eastern Australia: A Window on Ecology and Evolution of Dispersal in Streams.

Hughes JM, Huey JA, McLean AJ, Baggiano O - Insects (2011)

Predictions for population genetic variation under two contrasting demographic models; the Stream Hierarchy Model and the Patchy Recruitment Model (A–C); (D) Shows different interpretations of deviations from Hardy-Weinberg Equilibrium. Red squares indicate significant deviations.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4553437&req=5

f1-insects-02-00447: Predictions for population genetic variation under two contrasting demographic models; the Stream Hierarchy Model and the Patchy Recruitment Model (A–C); (D) Shows different interpretations of deviations from Hardy-Weinberg Equilibrium. Red squares indicate significant deviations.
Mentions: By designing sampling programs that included sites from both within the same stream, from different streams in the same subcatchments and from across catchment boundaries, it was possible to test these hypotheses. The idea was that if larval drift was the major mechanism of dispersal, then genetic variation should reflect the stream hierarchy, in other words, should fit the stream hierarchy model [15]. Samples from the same streams should be more similar than those from different subcatchments and those from different catchments should be greater again (Figure 1). Alternatively, if adult flight is the major mechanism of dispersal, then genetic differences between sites would reflect the straight line distance between them. An initial study using a freshwater shrimp that is limited to the stream network demonstrated that the stream hierarchy model was adhered to; with the greatest genetic differentiation between two catchments, with differentiation decreasing between sub-catchments and further between streams within sub-catchments and pools within streams [16]. The reverse effect was shown for three aquatic insect species: Bungona narilla, Tasiagma ciliata and Rheumatometra sp., which each showed the most differentiation between pools within a stream and the least across catchment boundaries [1,17,18]. Clearly, genetic variation in these species did not fit the stream hierarchy model. While this was assumed to imply that adult flight was the major dispersal mechanism, the result of large significant differences between pools within streams was unexpected. Further observations of the genetic data indicated that the differences were not consistent among genetic marker loci (allozymes) and that there were numerous samples that did not fit predictions of Hardy-Weinberg Equilibrium (HWE). These deviations did not occur consistently at particular sites or particular loci. These findings led to the suggestion that the results could result from the fact that pools did not contain a representative sample of the genetic diversity because they represented the offspring of a limited number of females and that larvae did not move much within the stream. The small number of families in each pool would explain both the deviations from Hardy-Weinberg predictions and apparent differences between streams. This idea was labeled the “patchy recruitment hypothesis” (PRH) [1].

Bottom Line: Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species.In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera.We conclude with a number of suggestions for further work.

View Article: PubMed Central - PubMed

Affiliation: Australian Rivers Institute and Griffith School of Environment, Griffith University, Nathan QLD 4111, Australia. jane.hughes@griffith.edu.au.

ABSTRACT
Studies of connectivity of natural populations are often conducted at different timescales. Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species. In contrast, studies conducted at historical timescales are usually more focused on evolutionary or biogeographic questions. In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera. We conclude that: (1) For both groups, the major mechanism of dispersal is by adult flight, with larval drift playing a very minor role and with unusual patterns of genetic structure at fine scales explained by the "patchy recruitment hypothesis"; (2) There is some evidence presented to suggest that at slightly larger spatial scales (~100 km) caddisflies may be slightly more connected than mayflies; (3) Examinations of three species at historical timescales showed that, in southeast Queensland Australia, despite there being no significant glaciation during the Pleistocene, there are clear impacts of Pleistocene climate changes on their genetic structure; and (4) The use of mitochondrial DNA sequence data has uncovered a number of cryptic species complexes in both trichopterans and ephemeropterans. We conclude with a number of suggestions for further work.

No MeSH data available.


Related in: MedlinePlus