Exaptation Traits for Megafaunal Mutualisms as a Factor in Plant Domestication

Abstract

Megafaunal extinctions are recurring events that cause evolutionary ripples, as cascades of secondary extinctions and shifting selective pressures reshape ecosystems. Megafaunal browsers and grazers are major ecosystem engineers, they: keep woody vegetation suppressed; are nitrogen cyclers; and serve as seed dispersers. Most angiosperms possess sets of physiological traits that allow for the fixation of mutualisms with megafauna; some of these traits appear to serve as exaptation (preadaptation) features for farming. As an easily recognized example, fleshy fruits are, an exaptation to agriculture, as they evolved to recruit a non-human disperser. We hypothesize that the traits of rapid annual growth, self-compatibility, heavy investment in reproduction, high plasticity (wide reaction norms), and rapid evolvability were part of an adaptive syndrome for megafaunal seed dispersal. We review the evolutionary importance that megafauna had for crop and weed progenitors and discuss possible ramifications of their extinction on: (1) seed dispersal; (2) population dynamics; and (3) habitat loss. Humans replaced some of the ecological services that had been lost as a result of late Quaternary extinctions and drove rapid evolutionary change resulting in domestication.

Central Argentina vegetation characteristics linked to extinct megafauna and some implications on human populations

“…The main categories of plants with endozoochorous seed dispersal (i.e. dispersing through animal ingestion) are those that produce: (I) large, fleshy fruits and (II) annual herbaceous plants with small seeds (Janzen, 1984; Janzen and Martin, 1982; Spengler, 2019; Spengler et al, 2021). Therefore, plants that evolve with contrasting mutualistic systems have a particular and diagnostic morphology.…”

Insularity and early domestication: anthropogenic ecosystems as habitat islands

“…A deeper consideration of the use of the term syndrome would be timely, as a number of domestication scholars are now arguing that there is no such thing as a domestication syndrome, in the sense that not all organisms express all traits of the syndrome in the same way (Lord et al 2019). What both domestication and island ecologists call a syndrome is really a complex set of convergent or parallel evolving traits (Fuller and Allaby 2009, Fuller et al 2014, Spengler 2020, Spengler et al 2021). Assuming these traits are adaptive, a solid understanding of the ecological factors that have facilitated convergence should clarify the elusive why and how questions of domestication.…”

“…Niche construction theory has also emerged as a sort of unifying process in domestication studies, but using the logic that all human behaviors can be clumped into one term – niche construction (Zeder and Smith 2009, Smith 2011). In this way, NCT simply serves as a flashy new banner to fit all cultivation or agricultural behaviors under, and does not contribute novel concepts to the debate (Spengler 2021).…”

Is Domestication Speciation? The Implications of a Messy Domestication Model in the Holocene

“…It can also be noted that polyploidy and genome duplication can lead to domestication, often more rapidly than the processes envisioned in the definitions and models of Fuller [16], Larson et al [7], and Meyer et al [17]. This is seen particularly in long-generation perennials, where self-incompatibility leads to higher rates of interspecific hybridization [19].…”