Lost a leg? No problem!

Cells keep a memory of their tissue origin during axolotl limb regeneration. Nature 460, 60-65 (2 July 2009)
During limb regeneration adult tissue is converted into a zone of undifferentiated progenitors called the blastema that reforms the diverse tissues of the limb. Previous experiments have led to wide acceptance that limb tissues dedifferentiate to form pluripotent cells. Here we have reexamined this question using an integrated GFP transgene to track the major limb tissues during limb regeneration in the salamander Ambystoma mexicanum (the axolotl). Surprisingly, we find that each tissue produces progenitor cells with restricted potential. Therefore, the blastema is a heterogeneous collection of restricted progenitor cells. On the basis of these findings, we further demonstrate that positional identity is a cell-type-specific property of blastema cells, in which cartilage-derived blastema cells harbour positional identity but Schwann-derived cells do not. Our results show that the complex phenomenon of limb regeneration can be achieved without complete dedifferentiation to a pluripotent state, a conclusion with important implications for regenerative medicine.

Invasive hybrid tiger salamanders impact native amphibians

Although the ecological consequences of species invasions are well studied, the ecological impacts of genetic introgression through hybridization are less understood. This is particularly true of the impacts of hybridization on “third party” community members not genetically involved in hybridization. We also know little about how direct interactions between hybrid and parental individuals influence fitness. Here, we examined the ecological effects of hybridization between the native, threatened California Tiger Salamander (Ambystoma californiense) and the introduced Barred Tiger Salamander (Ambystoma tigrinum mavortium). Native x introduced hybrids are widespread in California, where they are top predators in seasonal ponds. We examined the impacts of early generation hybrids (first two generations of parental crosses) and contemporary hybrids derived from ponds where hybrids have been under selection in the wild for 20 generations. We found that most classes of hybrid tiger salamander larvae dramatically reduced survival of two native community members, the Pacific Chorus Frog (Pseudacris regilla) and the California Newt (Taricha torosa). We also found that native A. californiense larvae were negatively impacted by the presence of hybrid larvae: Native survival and size at metamorphosis were reduced and time to metamorphosis was extended. We also observed a large influence of Mendelian dominance on size, metamorphic timing and predation rate of hybrid tiger salamanders. These results suggest that both genetic and ecological factors are likely to influence the dynamics of admixture, and that tiger salamander hybridization might constitute a threat to additional pond-breeding species of concern in the region.

Invasive hybrid tiger salamander genotypes impact native amphibians. PNAS USA June 29, 2009

The mystery of the legless frogs

Scientists think they have resolved one of the most controversial environmental issues of the past decade: the curious case of the missing frogs legs. Around the world, frogs are found with missing or misshaped limbs, a striking deformity that many researchers believe is caused by chemical pollution. However, tests on frogs and toads have revealed a more natural, benign cause. The deformed frogs are actually victims of the predatory habits of dragonfly nymphs, which eat the legs of tadpoles. In the late 1980s and early 1990s, researchers started getting reports of numerous wild frogs or toads being found with extra legs or arms, or with limbs that were partly formed or missing completely. The cause of these deformities soon became a hotly contested issue. Some researchers believed they might be caused naturally, by predators or parasites. Others thought that was highly unlikely, fearing that chemical pollution, or UV-B radiation caused by the thinning of the ozone layer, was triggering the deformations.

Meanwhile in Ecuador...

More on chytrid

Using itraconazole to clear Batrachochytrium dendrobatidis infection, and subsequent depigmentation of Alytes muletensis tadpoles.
Dis Aquat Organ. 2009 Feb 25;83(3):257-60
Batrachochytrium dendrobatidis (Bd) is a global threat to amphibian biodiversity. Current calls for conservation through captive breeding require that efficient and reliable antifungal treatments be developed for target species. Here we confirm that the antifungal itraconazole is an effective treatment for infection in larval Alytes muletensis (Mallorcan midwife toad). Exceptionally low doses applied as few as 7 times were effective at clearing infection from tadpoles for up to 28 days after treatment. However, we cannot recommend itraconazole as a treatment for this species as depigmentation of tadpoles was observed. Further research is required to determine the putative hepatotoxicity of this treatment.


Lack of Evidence for the Drought-linked Chytridiomycosis Hypothesis.
J Wildl Dis. 2009 Apr;45(2):537-41
A significant amount of recent research has focused on the potentially synergistic roles of climate change and disease in causing amphibian declines and extinctions. Herein I discuss the drought-linked chytridiomycosis hypothesis (DLCH), which states that prolonged or intensified dry seasons trigger or exacerbate epidemics of chytridiomycosis, a potentially lethal skin disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis. I demonstrate that the DLCH runs contrary to our knowledge of B. dendrobatidis physiology, biogeography, and host-parasite ecology and conclude that abnormally dry weather should actually favor amphibians by decreasing the prevalence, severity, and spread of chytridiomycosis.

Wild Dendrobate auratus in Costa Rica

Breakfast for the Brazils

I don't normally bother putting flies in a dish, but occasionally if a lot of crud comes out of the culture and mixes with the files I do in order to avoid too much getting in the viv. Still, it gave them a chance to be sociable :-)

Sobering discovery for Europe’s amphibians

A new report commissioned by the European Commission and carried out by IUCN highlights alarming declines for a range of frogs, toads, newts, snakes and lizards. The study shows that of Europe’s 85 species of amphibian, 23% now feature on the IUCN’s Red List of Threatened Species:

Overall, nearly a quarter of amphibians are considered threatened in Europe. A further 17% of amphibians are considered Near Threatened. By comparison, 19% of European reptiles, 15% of European mammals and 13% of European birds are threatened. No other groups have yet been comprehensively assessed at the European level. More than half of amphibians (59%) have declining populations. A further 36% are stable, and only 2% are increasing.
The overwhelming majority of threatened and Near Threatened amphibian species are endemic to both Europe and the EU, highlighting the responsibility that European countries have to protect the entire global populations of these species. All species considered threatened (Critically Endangered, Endangered, or Vulnerable) at the European level are endemic to Europe and are found nowhere else in the world.
Amphibian species richness is greatest at intermediate latitudes (France, Germany, Czech Republic) as well as in the south and on islands. Habitat loss, fragmentation and degradation are the most significant threats to amphibians in Europe. Other major threats include pollution (including global climate change caused by greenhouse gas emissions) and invasive alien species.

Tylototriton kweichowensis

Busy Saturday

Most weekends, Saturday is my main day in the frogroom, and in addition to the regular maintenance schedule, today seemed to be particularly busy:

• Two egg clutches from Dendrobates tinctorius Patricia and Dendrobates leucomelas
• Lots of new Mesotriton alpestris apanus larvae
• Set up some new rearing boxes for froglets:
  

But the funniest thing was moving an adult Dendrobates azureus female into a viv with a younger pair who haven't got the hang of the breeding thing yet. I wish I'd taken a video of the ensuing chaos. I had been slight;ly worried about the possibility that the females might fight, but instead, as soon as she clapped eyes on the male, she was after him, chasing him round the viv, stroking and generally behaving in a lustful fashion. He looked terrified!

I think I might be needing those new frog boxes soon :-)

Pacific Tree Frog - Pseudacris regilla

Pacific Tree Frog via kwout

Vivarium for sale

90 x 30 x 30cm (30 long x 12 wide x 12 inches), top opening vivarium.
Ventilated escape-proof lid, suitable for amphibians, reptiles, insects, rodents, etc.
£15, buyer collects from Leicester.

SOLD!