The Evolution of Defense Mechanisms Correlate with the Explosive Diversification of Autodigesting Coprinellus Mushrooms (Agaricales, Fungi)

Abstract

Bursts of diversification are known to have contributed significantly to the extant morphological and species diversity, but evidence for many of the theoretical predictions about adaptive radiations have remained contentious. Despite their tremendous diversity, patterns of evolutionary diversification and the contribution of explosive episodes in fungi are largely unknown. Here, using the genus Coprinellus (Psathyrellaceae, Agaricales) as a model, we report the first explosive fungal radiation and infer that the onset of the radiation correlates with a change from a multilayered to a much simpler defense structure on the fruiting bodies. We hypothesize that this change constitutes a key innovation, probably relaxing constraints on diversification imposed by nutritional investment into the development of protective tissues of fruiting bodies. Fossil calibration suggests that Coprinellus mushrooms radiated during the Miocene coinciding with global radiation of large grazing mammals following expansion of dry open grasslands. In addition to diversification rate-based methods, we test the hard polytomy hypothesis, by analyzing the resolvability of internal nodes of the backbone of the putative radiation using Reversible-Jump MCMC. We discuss potential applications and pitfalls of this approach as well as how biologically meaningful polytomies can be distinguished from alignment shortcomings. Our data provide insights into the nature of adaptive radiations in general by revealing a deceleration of morphological diversification through time. The dynamics of morphological diversification was approximated by obtaining the temporal distribution of state changes in discrete traits along the trees and comparing it with the tempo of lineage accumulation. We found that the number of state changes correlate with the number of lineages, even in parts of the tree with short internal branches, and peaks around the onset of the explosive radiation followed by a slowdown, most likely because of the decrease in available niches.

Radiation and repeated transoceanic dispersal of Schoeneae (Cyperaceae) through the southern hemisphere

“…Lewis et al (2005) developed a reversible‐jump Markov chain Monte Carlo (MCMC) procedure that enables sampling of trees with one or more polytomies during Bayesian phylogeny reconstruction. Although the motivation for this method was to prevent the inflation of support for nodes above very short branches (the “star tree paradox”), it also allows the posterior probability of a hard polytomy at a particular node to be calculated as the proportion of sampled trees with a polytomy at the position of interest (Nagy et al, 2012).…”

Is the switch to an ectomycorrhizal state an evolutionary key innovation in mushroom‐forming fungi? A case study in the Tricholomatineae (Agaricales)

“…Nagy et al. () studied the family Psathyrellaceae to identify morphological traits that could represent key innovations. Their results suggest that the loss of a veil (a protective tissue layer found on the fruiting bodies of some mushroom‐forming fungi) and the gain of hairs, which represent a transition to a new defense mechanism, might be correlated with an explosive radiation within this group.…”

Enhancing our understanding of anatomical diversity in Tomentella ectomycorrhizas: characterization of six new morphotypes

“…These special structures might have a kind of developmental or protective function as discussed for different cystidia of fruit bodies (e.g. Kües 2000;Clémencon 2004;Nagy et al 2011Nagy et al , 2012a. Agerer (2001) has interpreted the variable organization of emanating elements of ECM as representing possible different ecological functions.…”