Immune Indexes of Larks from Desert and Temperate Regions Show Weak Associations with Life History but Stronger Links to Environmental Variation in Microbial Abundance

Immune defense may vary as a result of trade-offs with other life-history traits or in parallel with variation in antigen levels in the environment. We studied lark species (Alaudidae) in the Arabian Desert and temperate Netherlands to test opposing predictions from these two hypotheses. Based on their slower pace of life, the trade-off hypothesis predicts relatively stronger immune defenses in desert larks compared with temperate larks. However, as predicted by the antigen exposure hypothesis, reduced microbial abundances in deserts should result in desert-living larks having relatively weaker immune defenses. We quantified host-independent and host-dependent microbial abundances of culturable microbes in ambient air and from the surfaces of birds. We measured components of immunity by quantifying concentrations of the acute-phase protein haptoglobin, natural antibody-mediated agglutination titers, complement-mediated lysis titers, and the microbicidal ability of whole blood. Desert-living larks were exposed to significantly lower concentrations of airborne microbes than temperate larks, and densities of some bird-associated microbes were also lower in desert species. Haptoglobin concentrations and lysis titers were also significantly lower in desert-living larks, but other immune indexes did not differ. Thus, contrary to the trade-off hypothesis, we found little evidence that a slow pace of life predicted increased immunological investment. In contrast, and in support of the antigen exposure hypothesis, associations between microbial exposure and some immune indexes were apparent. Measures of antigen exposure, including assessment of host-independent and host-dependent microbial assemblages, can provide novel insights into the mechanisms underlying immunological variation.

Markets misinterpreted? a comment on Sánchez-Amaro and Amici (2015)

In a recent essay, Sánchez-Amaro and Amici (2015) reviewed evidence in support of biological market theory (BMT) in primates. Since the pioneering work by Noë (1990, 1992; Noë, van Schaik, & van Hoof, 1991), and Barrett and colleagues (Barrett, Gaynor, & Henzi, 2002; Barrett, Henzi, Weingrill, Lycett, & Hill, 1999), several studies have looked for and found evidence of BMT in a variety of primate species, from lemurs (Norscia, Antonacci, & Palagi, 2009; Port, Clough, & Kappeler, 2009) to monkeys (Gumert 2007; Tiddi, Aureli, & Schino 2012; Fruteau, Lemoine, Hellard, van Damme & Noë, 2011) and apes (Koyama, Caws, & Aureli, 2012; Newton-Fisher & Lee, 2011; Kaburu & Newton-Fisher, 2015a, 2015b). With an increasingly large number of studies, a review such as the one by Sánchez-Amaro and Amici (2015) would be warmly welcome as a timely summary of the evidence for BMT, and an indication of future directions. The authors identify four areas of interest and usefully highlight some potential issues with BMT, for example where free trading is compromised by extortion or the need for comparable methods across studies. However, while their aims may be laudable, we feel there are particular flaws in some of their arguments and some misrepresentation of cited literature that we would like to correct