Intraspecific Variation in Growth and Reproduction of the Marine Leech, Heptacyclus buthi.

Heptacyclus buthi was harvested from fish hosts in rocky intertidal zones of Sonoma and Marin Counties, California, in October 2008 (n = 162) and October 2010 (n = 51). The size of the leeches was quantified using a method that approximated the sagittal cross-section of each specimen. Size-frequency curves were modeled to estimate the number of size-class cohorts in each year. If H. buthi is an annual species like many of its relatives, the single cohort modeled for in 2010 and the comparable "older" cohort in 2008, both with a broad range of sizes, may represent 1 component of its reproductive life history. A second, younger, more-numerous, less-variable cohort modeled from the 2008 sample may represent a second reproductive bout during that year that was prevented in the subsequent La Niña period of 2010-2011.

A Comparison of Isogenic Homozygous Clone and Wildtype Zebrafish (Danio rerio): Survival and Developmental Responses to Low pH Conditions.

The value of bioassays as analytical methods for assessing the potency of particular stressors on live animal models depends on the precision of their results, which are greatly influenced by the choice of test subjects. The genetic makeup of experimental subjects varies, and, as such, so will their responses to the test environment. Genetic diversity of test populations may contribute to statistical variability; therefore, the use of genetically similar subjects may enhance the utility of bioassays. This study addresses the efficacy of using isogenic homozygous zebrafish (Danio rerio) as subjects for bioassays. Stress responses (acidic conditions) were compared during early development for gynogenetically produced isogenic homozygous line of zebrafish (C32) and wildtype (WT) zebrafish. Experiments evaluated early life stage milestones after exposure to low pH in water of a different electrolyte composition. Because the isogenic homozygous clonal (IHC) fish possessed far less genetic variability than the WT fish tested, it was predicted that the IHC fish would exhibit less variability in their response to stress. Although we found no significant differences in the variability between the responses of the IHC and WT fish, pH and water hardness level had a differential effect on the two groups. Simple strain differences may be the probable cause of the response differences to environmental stress. Factors that may affect stress response, such as heterogeneity, co-adapted gene complexes, and domestication, are discussed. Our findings and review of recent zebrafish literature stress the need for researchers to carefully consider breeding histories and trait characteristics for each potential test subject to maximize the sensitivity of the assay.