Population Ecology I
Presiding: J Holomuzki, Ohio State University; L Baumgartner, University of Connecticut
NB51B-01 08:30h
Biological and Earth History as Revealed by Australian Subtropical Sand Islands
Off the coast of subtropical Queensland in Australia lie a series of large, forested sand islands. These islands have attracted the interest of geologists, hydrologists and biologists because of the sequential formation of ancient and recent dunes and the presence of abundant and varied freshwater ecosystems. These range from small coastal creeks, water-table "window" lakes and isolated "perched" lakes set well above the groundwater. These islands have only been separated from the mainland for a relatively short 6000 years or so and thus theoretically should display little differentiation from mainland populations. We sequenced two mitochondrial genes from the nearly omnipresent macroinvertebrate crustacean, Caridina indistincta, to investigate the nested island-within-island nature of freshwater-restricted taxa on these islands. This makes for potentially interesting biogeographic patterns between water bodies on islands, between islands and between the islands and the mainland. When phylogeographic patterns are related to geomorphological ones, inferences can be made about the methods, timing and direction of faunal colonisation and geologically induced vicariance. We discovered a series of lineages, ranging from cryptic species whose divergence considerably predates the islands themselves, to shallow differences within and between islands and the mainland. This highlights the complex biological and geological history of the area.
NB51B-02 08:45h
Population Diversity and Dispersal of Two Species of Stoneflies (Order Plecoptera) Within Four Watersheds of Northeastern Ohio.
This study investigates two species of stoneflies with potentially opposing dispersal capabilities and genetic structure within four watersheds in the Lake Erie drainage system of Northeast Ohio. This research is two fold; it provides information on genetic variation of two understudied aquatic invertebrate species and the impact of human land-use practices on this variation. Populations of Allocapnia recta, a winter emerging stonefly are predicted to have the least genetic variation within the four watersheds and most differences among sites due to its rudimentary wing structure and winter emergence. Leuctra tenuis is predicted to have greater genetic variability within sites and fewer differences among sites because of its higher migration potential. In both species, models of isolation by distance will be tested. Distinct polymorphisms exist within the 16s rRNA region of A. recta suggesting that this fragment has sufficient variation to address these questions.
NB51B-03 09:00h
A Translocation Gives Insight into the Effects of Hybridization Between wild Populations: Implications for Understanding the Distributions of Closely Related Species.
If two populations are separated for long enough in evolutionary time, mixing them may result in hybrids with reduced fitness. Possible consequences of this are the development of mechanisms that reduce the chance of hybridization or the extinction of one or other of the two genotypes. In 1995, a number of freshwater shrimp (Paratya australiensis) were translocated between two streams within the Brisbane River drainage. Later analysis of mitochndrial DNA revealed that the two populations were quite divergent genetically and had likely been separated for over 2 million years. Seven years after the translocation, the translocated genotype had sent the resident genotype extinct in the pool where the translocation took place, and in pools above and below in the stream. In this talk, I will present data from the next two generations and show that the translocated genotype has taken over all pools up-stream of the original site (a distance of over 2km), but has not become established more than 500 m below the site. Results suggest that survival of different genotypes within a generation are dependant on position in the stream (up-stream or downstream, but when fitness is calculated between generations, translocated genopyes are superior. Our findings will be related to a more general phylogeographic survey of the shrimp in eastern Australia.
NB51B-04 09:15h
Life History Variation in an Alpine Caddisfly: Local Adaptation or Phenotypic Plasticity?
Facultative species that inhabit permanent and temporary streams can be locally adapted to their stream of origin or exhibit life history plasticity. Temporary stream populations should respond to environmental cues signalling stream drying, whereas permanent stream populations may not. We used a common garden experiment to test whether males and females of an alpine caddisfly from six populations (3 permanent/3 temporary streams) differed in their life history responses to combined changes in photoperiod (ambient/late) and hydroperiod (constant/drying). Responses varied by sex, time-constraint cue and population. Both sexes shortened development time in the late photoperiod, and males emerged before females in all treatments. Growth rates were higher in the late photoperiod for both sexes, and females had higher growth rates and mass at emergence than males. Growth rate compensation in the late photoperiod resulted in similar masses at emergence for both photoperiods. Population-level differences in responses varied according to microgeographic co-gradient variation. Our results suggest that while stream drying cues may not exert sufficient selection pressure to promote faster development in temporary streams, populations may be locally adapted to differences in growing season length associated with stream-specific environmental characteristics.
NB51B-05 09:30h
Habitat-specific Tradeoffs Between Risk of Flow-induced Dislodgment and Fish Predation Affect Shell Morphologies of Potamopyrgus antipodarum in New Zealand
Smooth and spiny shell-morphs exist in populations of the mudsnail Potamopyrgus antipodarum in New Zealand streams and lakes. We estimated the relative frequencies of smooth and spiny shell-morphs from 11 rivers and 9 lakes on the South Island and used stepwise regression to identify environmental variables that affected shell-morph frequencies. Habitat (stream or lake) explained 57% of the variation in morph frequency. Nearly 70% of snails in streams were smooth-shelled, whereas >80% of snails in lakes were spiny. Results from flow tank experiments showed that spines collected seston (sloughing algae and leaf matter) at current speeds <40 cm/s, making spiny-morphs more prone to flow-induced dislodgment than smooth-morphs. Moreover, individuals with longer spines collected more seston, and hence were more susceptible to dislodgment, than those with shorter ones. However, an advantage of spines was lower predation rates by common bullies (Gobiomorphus cotidianus), a widespread benthic fish in New Zealand streams and lakes. All snails egested by bullies were dead, suggesting common bullies may help regulate mudsnail populations in nature. Our results suggest tradeoffs between susceptibility to flow-induced dislodgment and fish predation affect habitat-specific frequencies of shell morphologies for this snail.
NB51B-06 09:45h
Microbial Populations in Lithifying and Non-lithifying Microbial Mat Systems: Community Interactions with Chemical and Physical Ecology
The precipitation of calcium carbonate in microbial mat systems such as stromatolites creates a geological record of life. We cannot read that record, however, without understanding the mechanism of precipitation and lithification (the consolidation of loose sediment grains into solid rock). Several different groups of mat bacteria have been implicated in the precipitation and dissolution of calcium carbonate, most notably cyanobacteria, sulfate-reducing bacteria, aerobic heterotrophs, and sulfide-oxidizing bacteria. Through their metabolic activities, cyanobacteria and sulfate-reducing bacteria both facilitate precipitation, while heterotrophs and sulfide-oxidizing bacteria facilitate dissolution. These trends within the larger functional groups are further affected by within-group differences, such as the ability of some sulfate reducers to more fully oxidize carbon, which should also result in greater precipitation. Differential abilities within the microbial community may create the difference between mat systems that do and do not form lithified layers. Both the larger functional groups and the within-group changes are often phylogenetically predictable, and community analysis of lithifying and non-lithifying mat systems may provide some predictions as to which groups dominate lithification. Two research sites provide ideal study systems: a hypersaline lagoon in Eleuthera, Bahamas, where lithifying and non-lithifying mats coexist under similar physical and chemical environments, and the open marine stromatolites of Highborne Cay, Bahamas, which exhibit both lithifying and non-lithifying surfaces. The microbial communities of both microbial mat types from these two systems were analyzed to elucidate the population structure and examine differences between the communities. Given the very different mat systems growing under similar large-scale environments, the community structures are an interesting reflection of how microbes both affect and are affected by their environment.