Genetics and Molecular Biology of Mouse Pigmentation

The formation of mouse coat color is a relatively complex developmental process that is affected by a large number of mutations, both naturally occurring and induced. The cloning of the genes in which these mutations occur and the elucidation of the mechanisms by which these mutations disrupt the normal pigmentation pattern is leading to an understanding of the way interactions between gene products lead to a final phenotype.     

Protozoa in Planktonic Food Webs1,2

Protozoa are now being recognized as important members of planktonic food webs. This is due to the inclusion of microbial links in our paradigm of trophic relationships. Heterotrophic microflagellates and ciliates are major grazers of bacteria. They can stimulate production through nutrient recycling and can transform microbial production into larger particles, which are then available for macroconsumers. In this paper we add new groups, the small (< 20 μm) ciliates and myxotrophic flagellates, to the planktonic food web.     

Ready and Waiting: Delayed Hatching and Extended Incubation of Anamniotic Vertebrate Terrestrial Eggs

Some anamniotic aquatic vertebrates lay eggs in a terrestrialhabitat that is hostile to the survival of hatchings or larvae.These terrestrial eggs are ready and able to hatch at a particulardevelopmental time, but do not hatch until presented with suitableconditions for aquatic larval survival. Beyond this time, hatchingis possible whenever aquatic conditions occur. The durationof extended terrestrial incubation is dependent on the availabilityof energy for metabolism from the yolk. Extended incubationis useful for anamniotic eggs laid in terrestrial habitats whereconditions suitable for larval survival arrive with unpredictableor variable timing. Examples of anamniotes with delayed hatchingand extended terrestrial incubation can be found among teleostfishes, anurans, and caudate amphibians. This paper characterizesthe embryonic period, compares this mode with other forms ofdevelopmental plasticity in anamniotes, evaluates the constraintsand advantages of this life history mode, and examines how somefishes and amphibians are able to obtain the benefits of terrestrialityfor their eggs when the timing of the return to aquatic conditionsis not entirely predictable.     

Indirect effects of introduced trout on Cascades frogs (Rana cascadae) via shared aquatic prey

1. The introduction of trout to montane lakes has negatively affected amphibian populations across the western United States. In northern California’s Klamath–Siskiyou Mountains, introduced trout have diminished the distribution and abundance of a native ranid frog, Rana (=Lithobates) cascadae. This is primarily thought to be the result of predation on frog larvae. However, if trout feed on larval aquatic insects that are available to R. cascadae only after emergence, then resource competition may also affect this declining native amphibian. 2. Stomach contents of R. cascadae were compared between lakes that contained trout and those from which introduced trout were removed. Total prey mass in stomach contents relative to frog body mass was not significantly different between lakes with fish and fish‐removal lakes, but in the former R. cascadae consumed a smaller proportion of adult aquatic insects. The stomach contents of fish included larvae of aquatic insects that are, as adults, eaten by R. cascadae. 3. Rana cascadae consumed fewer caddisflies (Trichoptera) and more grasshoppers (Orthoptera) at lakes with higher densities of fish. At lakes with greater aquatic habitat complexity, R. cascadae consumed more water striders (Hemiptera: Gerridae) and terrestrial spiders (Araneae). 4. We suggest that reductions in the availability of emerging aquatic insects cause R. cascadae to consume more terrestrial prey where trout are present. Thus, introduced trout may influence native amphibians directly through predation and, indirectly, through pre‐emptive resource competition.     

Strong founder effects and low genetic diversity in introduced populations of Coqui frogs

The success of non-native species may depend on the genetic resources maintained through the invasion process. The Coqui ( Eleutherodactylus coqui ), a frog endemic to Puerto Rico, was introduced to Hawaii in the late 1980s via the horticulture trade, and has become an aggressive invader. To explore whether genetic diversity and population structure changed with the introduction, we assessed individuals from 15 populations across the Hawaiian Islands and 13 populations across Puerto Rico using six to nine polymorphic microsatellite loci and five dorsolateral colour patterns. Allelic richness ( R _T) and gene diversity were significantly higher in Puerto Rico than in Hawaii populations. Hawaii also had fewer colour patterns (two versus three to five per population) than Puerto Rico. We found no isolation by distance in the introduced range, even though it exists in the native range. Results suggest extensive mixing among frog populations across Hawaii, and that their spread has been facilitated by humans. Like previous research, our results suggest that Hawaiian Coquis were founded by individuals from sites around San Juan, but unlike previous research the colour pattern and molecular genetic data (nuclear and mtDNA) support two separate introductions, one on the island of Hawaii and one on Maui. Coquis are successful invaders in Hawaii despite the loss of genetic variation. Future introductions may increase genetic variation and potentially its range.