In a Northeastern U.S. forest, tiger salamanders were abundant. These salamander

Question

In a Northeastern U.S. forest, tiger salamanders were abundant. These salamanders need the humidity of the forest to survive and have a short dispersal distance when they leave the forest (less than 50 feet). A mall was built in the region and the forest was almost completely clear cut. 10 small forest fragments were left (1-10). Fragments 8, 9, 10 were located close to each other (less than 30 feet apart) and were bigger in size. The other seven were located more than 200 feet apart from each other and were smaller. The original salamander population now is split in the ten small forest fragments. a. In which forest fragment(s) will likely genetic drift have a higher impact on the salamander population? Explain. b. Which fragment will likely have a lower genetic variation within the salamander population? Explain. c. Which salamander populations will likely be genetically different from each other? Which ones will likely be more similar? Explain.

Explanation / Answer

a)

Habitat fragmentation poses a serious threat to plants through genetic changes associated with increased isolation and reduced population size. However, the longevity of trees, combined with effective seed or pollen dispersal, can enhance their resistance to these effects. The European beech (Fagus sylvatica) dominates forest over large regions of Europe. We demonstrate that habitat fragmentation in this species has led to genetic bottlenecks and the disruption of the species' breeding system, leading to significantly elevated levels of inbreeding, population divergence, and reduced genetic diversity within populations. These results show that, in contrast with the findings of previous studies, forest fragmentation has a negative genetic impact, even in this widespread, wind-pollinated tree. The identification of significant effects of forest fragmentation in beech demonstrates that trees are not at reduced risk from environmental change. This should be accounted for in the management of remaining natural and seminatural forest throughout the world.

b)

Combining phylogeographic data from mitochondrial DNA (mtDNA) of Nearctic and Palearctic freshwater and anadromous fishes, we used a comparative approach to assess the influence of historical events on evolutionary patterns and processes in regional fish faunas. Specifically, we (i) determined whether regional faunas differentially affected by Pleistocene glaciations show predictable differences in phylogeographic patterns; (ii) evaluated how processes of divergence and speciation have been influenced by such differential responses; and (iii) assessed the general contribution of phylogeographic studies to conservation issues. Comparisons among case studies revealed fundamental differences in phylogeographic patterns among regional faunas. Tree topologies were typically deeper for species from nonglaciated regions compared to northern species, whereas species with partially glaciated ranges were intermediate in their characteristics. Phylogeographic patterns were strikingly similar among southern species, whereas species in glaciated areas showed reduced concordance. The extent and locations of secondary contact among mtDNA lineages varied greatly among northern species, resulting in reduced intraspecific concordance of genetic markers for some northern species. Regression analysis of phylogeographic data for 42 species revealed significant latitudinal shifts in intraspecific genetic diversity. Both relative nucleotide diversity and estimates of evolutionary effective population size showed significant breakpoints matching the median latitude for the southern limit of the Pleistocene glaciations. Similarly, analysis of clade depth of phylogenetically distinct lineages vs. area occupied showed that evolutionary dispersal rates of species from glaciated and nonglaciated regions differed by two orders of magnitude. A negative relationship was also found between sequence divergence among sister species as a function of their median distributional latitude, indicating that recent bursts of speciation events have occurred in deglaciated habitats. Phylogeographic evidence for parallel evolution of sympatric northern species pairs in postglacial times suggested that differentiation of cospecific morphotypes may be driven by ecological release. Altogether, these results demonstrate that comparative phylogeography can be used to evaluate not only phylogeographic patterns but also evolutionary processes. As well as having significant implications for conservation programs, this approach enables new avenues of research for examining the regional, historical, and ecological factors involved in shaping intraspecific genetic diversity.

c)salamander populations

When Katie O'Donnell put on her first pair of heavy duty knee pads and crawled through Missouri forests in 2010, she found more than she was looking for.

Grubbing in the leaves for red-backed salamanders was part of an MU research project that concluded there were far more of the amphibians than previously believed in forests of the Missouri Ozarks.

The researchers estimated red-backed salamander populations were up to two to four times higher than previous estimates. Salamanders were described as one of the largest sources of food of all vertebrates in the forest when previous population studies were published in the 1970s.

O'Donnell, a graduate student at MU, helped with the research and statistical analysis. The results, coming from samples collected by O'Donnell in 2010 and 2011, are a closer estimate than the earlier research.

"There's been this trend to tackle the issue of imperfect detection," O'Donnell said.

The research involved in-depth sampling and statistical methods not used in the past, which contributed to the higher and likely more accurate estimate, O'Donnell said.

In the previous study, salamanders were counted when seen, and plotted on a grid to estimate abundance. The new study took into account factors such as the nocturnal nature of salamanders and their tendency to live underground, O'Donnell said.

"Oftentimes when people are looking for salamander, they only look under natural cover objects," O'Donnell said, which neglects leaf litter and other places the amphibians tend to hide.

During the research, conducted in the spring and fall of 2010 and 2011 in the Mark Twain National Forest about 130 miles southeast of Columbia, O'Donnell manually counted sightings at test sites by uncovering rocks and digging through leaves. The new estimate is considered more accurate partly due to this diligence.

Ray Semlitsch, an MU biology professor who led the research, said salamanders provide food for other creatures such as birds, racoons, snakes and other mammals and reptiles. Salamanders, on the other hand, have an appetite for insects.

High salamander populations likely mean greater control of leaf-litter invertebrates, such as spiders and termites, which can increase carbon content in the air if uncontrolled, Semlitsch said. Salamanders and other amphibians also assist in soil enrichment, he said.

Many of these benefits are still speculative, Semlitsch said.

"We can't really say what the role of salamanders are based on this study," Semlitsch said. "It's just an enormous amount of biomass out there."

The large amount of biomass indicates salamander populations play an important role in the forest ecosystem, Briggler said, making conservation efforts important.

Acknowledging salamanders as a main food source for forest populations may drive research and conservation efforts, Semlitsch said.

Future research on the effects of salamander biomass is necessary to obtain insights on the importance of the salamander population in forest ecosystems, Semlitsch said. "This is a small piece of a puzzle that we need to understand.

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