DOI: 10.5061/dryad.qnk98sfjg
title: A Double-Edged Sword: Parental care increases risk of offspring infection by a maternally-vectored parasite

description: Parental care can protect offspring from predators but can also create
 opportunities for parents to vector parasites to their offspring. We
 hypothesized that the risk of infection by maternally-vectored parasites
 would increase with the frequency of mother-offspring contact. Ammophila
 spp. wasps (Hymenoptera: Sphecidae) build nests in which they rear single
 offspring. Ammophila species exhibit varied offspring provisioning
 behaviors: some species enter the nest once to provision a single, large
 caterpillar, whereas others enter the nest repeatedly to provision with
 many smaller caterpillars. We hypothesized that each nest visit increases
 the risk of offspring parasitism by Paraxenos lugubris (Strepsiptera:
 Xenidae), whose infectious stages ride on the mother wasp (phoresy) to
 reach the vulnerable Ammophila offspring. We quantified parasitism risk by
 external examination of museum-curated Ammophila specimens—the anterior
 portion of P. lugubris protrudes between the adult host’s abdominal
 sclerites and reflects infection during the larval stage. As predicted,
 Ammophila species that receive larger numbers of provisions incur greater
 risks of parasitism, with nest provisioning behavior explaining ca. 90% of
 the interspecific variation in mean parasitism. These findings demonstrate
 that parental care can augment, rather than reduce, risk of parasite
 transmission to offspring.
description: We gathered records of the provisioning behavior for Californian
 species of <em>Ammophila </em>from the literature. Using
 “<em>Ammophila</em>” and “provisioning” as terms, we conducted
 searches via the Web of Science, BIOSIS, and Google Scholar search
 engines. We supplemented the published literature with our own unpublished
 field observations. When multiple provisioning records existed for a
 species, we calculated an average across the studies to produce a single
 estimate for the mean prey provisioned. These data were
 gathered via examination of all specimens of
 <em>Ammophila</em> housed in the Bohart Museum of Entomology,
 University of California, Davis. Parasitized <em>Ammophila
 </em>specimens stored in the Strepsiptera collections were also
 included in our dataset. <em>Paraxenos lugubris</em> develops
 as an endoparasite, but its anterior end protrudes visibly from the
 abdomen of its host as it completes its development, allowing parasitism
 to be recorded in museum-preserved specimens. We examined each specimen
 with a stereomicroscope and scored for the presence or absence of
 <em>Paraxenos</em>. Wasps were scored as parasitized when they
 had a female <em>Paraxenos</em> still present in their
 abdomen, or when they had a male <em>Paraxenos </em>either
 still present and enclosed in a pupal casing, or previously-emerged from
 the abdomen, leaving behind a still-visible pupal exoskeleton (winged
 males emerge from their host to seek out females for mating, whereas the
 wingless females never leave their hosts). We also recorded
 <em>Ammophila </em>wing length as an index of host size, and
 the collection date for each specimen. Our final data set included all 16
 species for which established estimates of mean prey provisioned were
 available. We scored a total of 8957 specimens collected between 1902 and
 2009. All data were recorded in Excel, and the spreadsheet plus its
 metadata are available here. Parasitism data were
 analyzed with a generalized linear mixed model with binomial variance and
 a logistic link function, using the R package
 <em>lme4. </em>An additional analysis involving phylogenetic
 contrasts run with the R package <em>ape </em>is included as
 an R script. A third R script contains the code for each visualized linear
 analysis. View README.txt for details about necessary R package
 versions.
description: In the document “ammophila_strep_project.csv”, null or 0 values
 should be left blank (with the exception of 0 values in columns
 "parasitism", "m_strep", and "f_strep"). One
 README file is available detailing the package versions used for each of
 the R scripts in this collection. Metadata/data description is available
 as a tab in the raw data Excel file.