Divergent oviposition preferences of sister species are not driven by nest survival: the evidence for neutrality

Abstract

Both adaptive and neutral trait evolution can contribute to divergence, but the relative contributions of the two remain unclear. Oviposition preference, a trait that has been demonstrated to contribute to divergence among populations, is often presumed to be an adaptive trait. Few studies explicitly test this assumption, however, and several researchers have demonstrated non-adaptive oviposition preferences in wildlife populations. In this study, we test whether adaptive divergence can explain current differences in the oviposition preferences of two sister species. In 2012 and 2013, we conducted a demographic study of sympatrically breeding populations of two sparrow species (Ammodramus caudacutus and Ammodramus nelsoni) and measured vegetation characteristics at nest and non-nest points. We found evidence for oviposition preference in both species and significant differences between the species' preferences. The vegetation characteristics that vary between species did not predict nest survival or offspring production, however. Our results provide an example of oviposition preference at a population level that appears non-adaptive as measured by productivity. We discuss other mechanisms by which oviposition preference can be adaptive, and make a case for the role of neutral evolution in shaping the oviposition preferences of these species. If divergence in oviposition preference is at least periodically neutral, as we hypothesize, such differences could provide fodder for future adaptation or reproductive isolation among populations.

Plasticity in nesting adaptations of a tidal marsh endemic bird

“…Specifically, successful nests were built higher in the vegetation, had more canopy cover, and were in higher elevation areas of the marsh than those that flooded. Several previous studies failed to find a consistent relationship between nest structures and nest success, despite strong evidence of nest site selection preferences for characteristics that confer resistance to flooding (Gjerdrum et al., ; Humphreys et al., ; Ruskin et al., ; Shriver et al., ). Our findings are consistent with these nest characteristics having a fitness effect, and the large sample size in our study (536 nests vs. 69 −160 nests in prior studies) may have allowed more power to detect small effect sizes.…”

“…Nest site selection is spatially random with respect to other nesting females (Bayard & Elphick, ; Gjerdrum et al., ), suggesting that structural characteristics of the nest itself may be more important to success than where the nest is located within the preferred nesting habitat (Gjerdrum et al., ). While prior research has found vegetation cover characteristics to be important in nest site selection, neither these vegetation characteristics, nor nest height (the height at which the nest is placed above the ground) and substrate elevation (the elevation of the marsh surface; see Figure ) have been found to consistently influence nest success (Gjerdrum et al., ; Humphreys, Elphick, Gjerdrum, & Rubega, ; Ruskin, Hodgman, Etterson, & Olsen, ; Shriver et al., ).…”

“…For nests to escape flooding, tidal water levels will rise above the marsh surface, but will not exceed the height of the nest. The canopy may help to retain eggs in a flooded nest 2005; Humphreys, Elphick, Gjerdrum, & Rubega, 2007;Ruskin, Hodgman, Etterson, & Olsen, 2015;Shriver et al, 2007).…”

Mechanistic modeling of insecticide risks to breeding birds in North American agroecosystems

“…Etterson et al [ 24 ] compared two versions of the parameterized MCnest model to field-based predictions of the number of broods per female produced in Illinois populations of Eastern meadowlark ( Sturnella magna ) and dickcissel ( Spiza americana ). The Markov algorithm behind MCnest has also been adapted for use as a multistate competing risks estimation model and has been applied to the problem of estimation of stressor effects on wild bird populations [ 53 – 55 ], including two cases exploring the effects of environmental contaminants [ 56 , 57 ]. Etterson [ 4 ] also showed how the framework could be further adapted to estimate acute mortality of contaminants in field trials when carcass scavenging and imperfect detection make inference difficult.…”

Extrinsic and intrinsic factors influence fitness in an avian hybrid zone

“…When chicks died during nest flooding or predation events, we obtained tissue samples when possible. We determined nest failure or success based on evidence at the nest site (Ruskin et al, 2015). Briefly, we considered a nest successful if it was found empty when at least one nestling would have been 10 days old; we counted a nest successful if at least one chick fledged.…”