How Metamorphosis Is Different in Plethodontids: Larval Life History Perspectives on Life-Cycle Evolution.

Plethodontid salamanders exhibit biphasic, larval form paedomorphic, and direct developing life cycles. This diversity of developmental strategies exceeds that of any other family of terrestrial vertebrate. Here we compare patterns of larval development among the three divergent lineages of biphasic plethodontids and other salamanders.

Phylogeny of Mental Glands, Revisited.

Mental glands and their associated delivery behaviors during courtship are unique to the plethodontid salamanders. Because previous interpretations of the evolution of these features were conducted using older phylogenetic hypotheses, we reanalyzed these traits with newer courtship descriptions and contemporary phylogenetic methods. Using Bayesian ancestral state reconstruction methods that have been developed since the first phylogenetic analyses were conducted in the mid-1990s, we reconstructed mental gland and courtship behavior evolution on a Bayesian phylogeny of the nuclear gene The most probable ancestral condition for plethodontids was resolved as presence of a mental gland.

Experimental Analysis of Allocation during Larval Development in Ambystomatid Salamanders.

We examined how variation in food availability and temperature influences patterns of energy allocation to growth, storage, metamorphosis, and reproduction in larval and . In each species, an allocation vector consisting of metamorphic size, duration of larval period, fat body mass, and gonad mass was influenced by both food and temperature. Larvae grew rapidly at high food levels and high temperature, and delayed metamorphosis when grown at low temperature.

Induction of Metamorphosis Causes Differences in Sex-Specific Allocation Patterns in Axolotls () that Have Different Growth Histories.

We tested the hypothesis that salamanders growing at different rates would have allocation patterns that differ among male and female metamorphic and larval salamanders. We raised individual axolotls, , on four food regimes: constant high growth (throughout the experiment), constant low growth (restricted throughout the experiment), high growth switched to low growth (ad libitum switched after 140 d to restricted), and low growth switched to high growth (restricted switched after 140 d to ad libitum). Because axolotls are obligate paedomorphs, we exposed half of the salamanders to thyroid hormone to induce metamorphosis.

Increased Larval Density Induces Accelerated Metamorphosis Independently of Growth Rate in the Frog .

We grew larval at different densities but maintained equal mean growth rates among density treatments (via equal per capita food levels) to test the hypothesis that larval density can influence metamorphic timing independently of larval growth rate. Tadpoles at high density metamorphosed earlier than tadpoles at low density despite growing at similar rates. Food reductions did not accelerate metamorphosis.

Transcriptional response of Mexican axolotls to Ambystoma tigrinum virus (ATV) infection.

Background: Very little is known about the immunological responses of amphibians to pathogens that are causing global population declines. We used a custom microarray gene chip to characterize gene expression responses of axolotls (Ambystoma mexicanum) to an emerging viral pathogen, Ambystoma tigrinum virus (ATV).

Result: At 0, 24, 72, and 144 hours post-infection, spleen and lung samples were removed for estimation of host mRNA abundance and viral load.

Effect of thyroid hormone concentration on the transcriptional response underlying induced metamorphosis in the Mexican axolotl (Ambystoma).

Background: Thyroid hormones (TH) induce gene expression programs that orchestrate amphibian metamorphosis. In contrast to anurans, many salamanders do not undergo metamorphosis in nature. However, they can be induced to undergo metamorphosis via exposure to thyroxine (T4).

Early gene expression during natural spinal cord regeneration in the salamander Ambystoma mexicanum.

In contrast to mammals, salamanders have a remarkable ability to regenerate their spinal cord and recover full movement and function after tail amputation. To identify genes that may be associated with this greater regenerative ability, we designed an oligonucleotide microarray and profiled early gene expression during natural spinal cord regeneration in Ambystoma mexicanum. We sampled tissue at five early time points after tail amputation and identified genes that registered significant changes in mRNA abundance during the first 7 days of regeneration.

Microarray analysis identifies keratin loci as sensitive biomarkers for thyroid hormone disruption in the salamander Ambystoma mexicanum.

Ambystomatid salamanders offer several advantages for endocrine disruption research, including genomic and bioinformatics resources, an accessible laboratory model (Ambystoma mexicanum), and natural lineages that are broadly distributed among North American habitats. We used microarray analysis to measure the relative abundance of transcripts isolated from A. mexicanum epidermis (skin) after exogenous application of thyroid hormone (TH).