Contrasting latitudinal gradients of body size in helminth parasites and their hosts

Tad Dallas*, Alyssa Lois M. Gehman, A. Alonso Aguirre, Sarah A. Budischak, John M. Drake, Maxwell J. Farrell, Ria Ghai, Shan Huang, Ignacio Morales-Castilla

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


Aim: We examined body size scaling relationships for two developmental life stages of parasitic helminths (egg and adult) separately in relationship to latitude (i.e. Bergmann's rule), temperature and temperature seasonality. Given that helminth eggs experience environmental conditions more directly, whereas adults live inside infected host individuals, we predict stronger environmentally driven gradients of body size for eggs than for adults. Location: Global. Time period: Present day. Major taxa studied: Parasitic helminths. Methods: We compiled egg size and adult body size data (both minimum and maximum) for 265 parasitic helminth species from the literature, along with species latitudinal distribution information using an extensive global helminth occurrence database. We then examined how the average helminth egg and adult body size of all helminth species present (minimum and maximum separately) scaled with latitude, temperature and temperature variability, using generalized linear models. Results: Both the egg size and the adult body size of helminths tended to decrease towards higher latitudes, although we found the opposite body size scaling pattern for their host species. Helminth sizes were also positively correlated with temperature and negatively, but more weakly, with temperature seasonality. Main conclusions: Instead of following the body size patterns of their hosts, helminth parasites are more similar to other ectotherms in that they follow the converse Bergmann's rule. This pattern did not differ between helminth developmental stages, suggesting that mean annual temperature and seasonality are unlikely to be related mechanistically to body size variation in this case.

Original languageEnglish
Pages (from-to)804-813
Number of pages10
JournalGlobal Ecology and Biogeography
Issue number6
Publication statusPublished - Jun 2019

Bibliographical note

Funding Information:
This study is supported by the U.S. National Science Foundation Research Coordination Network (NSF/NIH/USDA DEB 131223). I.M.‐C. receives funding from University of Alcalá (Programa de Ayudas Postdoctorales de la Universidad de Alcalá). S.H. receives funding from the Alexander von Humboldt Foundation through a postdoctoral fellowship. A.‐L.M.G. received funding from the National Science Foundation Postdoctoral Fellowship in Biology. T.A.D. recevied funding through the Research Centre for Ecological Change, which is funded by the Jane and Aatos Erkko Foundation.

Publisher Copyright:
© 2019 John Wiley & Sons Ltd


  • Bergmann’s rule
  • helminth size distribution
  • host–parasite interactions
  • latitude–size relationship
  • parasite macroecology
  • temperature–size relationship

ASJC Scopus subject areas

  • Global and Planetary Change
  • Ecology, Evolution, Behavior and Systematics
  • Ecology


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