and population genetic effects. Balkenhol and Waits (2009) found that 76% of
the 33 reviewed studies employed these markers in road ecology studies (see
below for railway studies). Indeed, authors who used mitochondrial analyses
failed to find genetic structuring related to railway-related barrier effects, as
happened with the Mongolian gazelle (Okada et al. 2012).
The easiest design consists of sampling individuals at both sides of a railway to
infer whether this acts as a barrier driving population differentiation. This
approach was used by Gerlach and Musolf (2000) to study the genetic substructuring between bank vole (Clethrionomys glareolus) populations bisected
by a railway in Germany and Switzerland. The authors found that a 40-year-old
railway did not contribute to genetic substructuring in bank voles. In their study
in the USA with the marbled salamander (Ambystoma opacum) in the USA,
Bartoszek and Greenwald (2009) found that the populations from two ponds
just separated by a railway, although potentially connected by a culvert, were
genetically differentiated, although some gene flow was still occurring. On the
contrary, the Qinghai-Tibetan railway seems not to be a barrier structuring the
toad-headed lizard (Phrynocephalus vlangalii) populations, as samples from
both sides of the railway were genetically similar, whereas those sampled at
20 km away were different, as expected due to the distance (Hu et al. 2012).
Genetics should be complemented with landscape analyses to control, among
other things, for the relationship between genetic and geographic distances. Reh
and Seitz (1990), using a sample design that included several sites and enzyme
analyses, found that railways contributed to the isolation, and thus the
inbreeding, of common frogs (Rana temporaria) in Germany. Yang et al.
(2011) used landscape analysis and genetics based on microsatellites to identify
the factors influencing the differentiation among Przewalski’s gazelle
(P. przewalskii) populations in China. Prunier et al. (2014) used a microsatellite
individual-based sampling scheme combined with computer simulations to
determine whether HSR in west-central France was old enough to cause genetic
discontinuities in the alpine newt (Ichthyosaura alpestris). The latter authors
did not detect any barrier effects, which could be due both to the relatively
recent existence of the railway (29 years), or to the highly nomadic behavior of
this amphibian. Also, the small size of newts could allow them to move under
the rails, minimizing their risk of being railway-killed. The few smooth newts
(Lissotriton vulgaris), a species of similar size, that were found railway-killed
in Poland, were found at pedestrian crossings, where newts are forced to move
over instead of under the rails (Kaczmarski and Kaczmarek 2016). On the other
hand, the simultaneous use of genetic approaches and landscape analyses has
also shown that linear infrastructures can, in some cases, increase connectivity.
For instance, the use of microsatellites enabled Fenderson et al. (2014) to
identify railways, powerlines, or even road sides as dispersal facilitators of New
England cottontails (Sylvilagus transitionalis), but their approach was limited
as they did not evaluate the relative importance of each of these infrastructures
to the observed increase in connectivity. Such an increase in the landscape
52
R. Barrientos and L. Borda-de-Água
the 33 reviewed studies employed these markers in road ecology studies (see
below for railway studies). Indeed, authors who used mitochondrial analyses
failed to find genetic structuring related to railway-related barrier effects, as
happened with the Mongolian gazelle (Okada et al. 2012).
The easiest design consists of sampling individuals at both sides of a railway to
infer whether this acts as a barrier driving population differentiation. This
approach was used by Gerlach and Musolf (2000) to study the genetic substructuring between bank vole (Clethrionomys glareolus) populations bisected
by a railway in Germany and Switzerland. The authors found that a 40-year-old
railway did not contribute to genetic substructuring in bank voles. In their study
in the USA with the marbled salamander (Ambystoma opacum) in the USA,
Bartoszek and Greenwald (2009) found that the populations from two ponds
just separated by a railway, although potentially connected by a culvert, were
genetically differentiated, although some gene flow was still occurring. On the
contrary, the Qinghai-Tibetan railway seems not to be a barrier structuring the
toad-headed lizard (Phrynocephalus vlangalii) populations, as samples from
both sides of the railway were genetically similar, whereas those sampled at
20 km away were different, as expected due to the distance (Hu et al. 2012).
Genetics should be complemented with landscape analyses to control, among
other things, for the relationship between genetic and geographic distances. Reh
and Seitz (1990), using a sample design that included several sites and enzyme
analyses, found that railways contributed to the isolation, and thus the
inbreeding, of common frogs (Rana temporaria) in Germany. Yang et al.
(2011) used landscape analysis and genetics based on microsatellites to identify
the factors influencing the differentiation among Przewalski’s gazelle
(P. przewalskii) populations in China. Prunier et al. (2014) used a microsatellite
individual-based sampling scheme combined with computer simulations to
determine whether HSR in west-central France was old enough to cause genetic
discontinuities in the alpine newt (Ichthyosaura alpestris). The latter authors
did not detect any barrier effects, which could be due both to the relatively
recent existence of the railway (29 years), or to the highly nomadic behavior of
this amphibian. Also, the small size of newts could allow them to move under
the rails, minimizing their risk of being railway-killed. The few smooth newts
(Lissotriton vulgaris), a species of similar size, that were found railway-killed
in Poland, were found at pedestrian crossings, where newts are forced to move
over instead of under the rails (Kaczmarski and Kaczmarek 2016). On the other
hand, the simultaneous use of genetic approaches and landscape analyses has
also shown that linear infrastructures can, in some cases, increase connectivity.
For instance, the use of microsatellites enabled Fenderson et al. (2014) to
identify railways, powerlines, or even road sides as dispersal facilitators of New
England cottontails (Sylvilagus transitionalis), but their approach was limited
as they did not evaluate the relative importance of each of these infrastructures
to the observed increase in connectivity. Such an increase in the landscape
52
R. Barrientos and L. Borda-de-Água