Pre- and post-association barriers to host switching in sympatric mutualists

Coevolution between mutualists can lead to reciprocal specialization, potentially causing barriers to host switching.  In the present study, we conducted assays to identify pre- and post-association barriers to host switching by endosymbiotic bacteria, both within and between two sympatric nematode clades.  In nature, Steinernema nematodes and Xenorhabdus bacteria form an obligate mutualism.  Free-living juvenile nematodes carry Xenorhabdus in a specialized intestinal receptacle.  When nematodes enter an insect, they release the bacteria into the insect hemocoel.  The bacteria aid in killing the insect and facilitate nematode reproduction.  Prior to dispersing from the insect, juvenile nematodes must form an association with their symbionts; the bacteria must adhere to the intestinal receptacle.  We tested for pre-association barriers by comparing the effects of bacterial strains on native verses non-native nematodes via their virulence towards, nutritional support of, and ability to as..., Data Collection
 
In vitro development assays were conducted on two types of media to differentiate bacterial virulence towards (LKA media) or nutritional support (LA media) of the nematodes.  For each media type, three nematode isolates carrying their native symbionts were tested on lawns of 6 strains of bacteria. Five replicates of each combination was observed daily for 8 days.  For in vivo association assays,we infected each Galleria mellonella caterpillar by pipetting 100 nematodes in 500uL of ddH2O on to the dorsum of the caterpillar. For pre-association assays, the nematodes were axenic, and bacteria cultures were injected into the caterpillars 24 hours after nematode infection.  For post-association assays, the nematodes were assumed to be carrying bacteria.  Infection success (Infection_Success) was measured as the proportion of infected caterpillars with any nematode emergence.  Mean nematode emergence (Estimated_IJ_Count) was estimated by volumetric subsampling.  We estimated..., , # Pre- and post-association barriers to host switching in sympatric mutualists

[https://doi.org/10.5061/dryad.0rxwdbs2f](https://doi.org/10.5061/dryad.0rxwdbs2f)

## Description of the data and file structure

The data file “JEB in vitro assay dataset.csv” contains 8 columns:

A.    Nematode: factor, no unit (Affine, Kraussei): the name of the nematode species used in the infection (*Steinernema affine *or *Steinernema kraussei*)

B.    Bacteria: factor , no unit (226, 235, 239, 266, 233, 241) description of the nematode isolate from which the bacteria was cultured.  226 and 235 are *S. affine*, 239 and 266 are *S. kraussei*, 233 and 241 are *S. texanum*

C.    Media_Type: factor, no unit (LA, LKA): descriptor of the type of media used for the assay, LA is lipid agar, and is used for the nutrition assay; LKA is liver-kidney agar, and is used for the virulence assay.

D.    Day: factor, day (0-8): the census day for each observation.

E.    N_Plates: numeric, plates  (1-10): the number...