Geographic and Temporal Variation of Distinct Intracellular Endosymbiont Strains of Wolbachia sp. in the Grasshopper Chorthippus parallelus: a Frequency-Dependent Mechanism?

Wolbachia is an intracellular endosymbiont that can produce a range of effects on host fitness, but the temporal dynamics of Wolbachia strains have rarely been experimentally evaluated. We compare interannual strain frequencies along a geographical region for understanding the forces that shape Wolbachia strain frequency in natural populations of its host, Chorthippus parallelus (Orthoptera, Acrididae). General linear models show that strain frequency changes significantly across geographical and temporal scales. Computer simulation allows to reject the compatibility of the observed patterns with either genetic drift or sampling errors. We use consecutive years to estimate total Wolbachia strain fitness. Our estimation of Wolbachia fitness is significant in most cases, within locality and between consecutive years, following a negatively frequency-dependent trend. Wolbachia spp. B and F strains show a temporal pattern of variation that is compatible with a negative frequency-dependent natural selection mechanism. Our results suggest that such a mechanism should be at least considered in future experimental and theoretical research strategies that attempt to understand Wolbachia biodiversity.

Isotopic effects of different preservation methods on scales of olive ridley sea turtles (Lepidochelys olivacea) from the Mexican Central Pacific.

RATIONALE: Stable isotope analysis can be used to obtain information on olive ridley sea turtles in the Mexican Central Pacific (MCP). Tissue samples such as scale, muscle, and blood are usually not analyzed immediately and are preserved in different substances such as ethanol, formalin, sodium chloride, the ideal being liquid nitrogen. Due to logistical reasons, the latter preservation method cannot always be used. The objective of the present study was to evaluate the efficiency of dimethyl sulfoxide (DMSO) as a preservation agent for later stable isotope analysis. METHODS: Forty-eight paired scale samples of olive ridley were collected in MCP waters and preserved in DMSO and liquid nitrogen. We determined their δ13 C and δ15 N values using a Carlo Erba 1108 elemental analyzer coupled to a ThermoFinnigan Delta Plus XP isotope ratio mass spectrometer (precision ±0.2‰ for each stable isotope). The mean isotopic ratios of each preservation method were compared. RESULTS: Significant differences were observed between the isotopic ratios of samples in the two preservatives. Samples preserved in DMSO resulted in more negative isotopic values than those in liquid nitrogen, and a correction factor was calculated. The correction factors were 2.1‰ for δ13 C values and 0.8‰ for δ15 N values. CONCLUSIONS: DMSO is not equivalent to liquid nitrogen for the preservation of olive ridley scales to be used for isotopic analysis. If DMSO has to be used for logistical reasons a replicate sample should also be collected to be able to estimate a correction factor. Copyright © 2016 John Wiley & Sons, Ltd.