Anthropogenic extinction threats and future loss of evolutionary history in reef corals

Abstract

Extinction always results in loss of phylogenetic diversity (PD), but phylogenetically selective extinctions have long been thought to disproportionately reduce PD. Recent simulations show that tree shapes also play an important role in determining the magnitude of PD loss, potentially offsetting the effects of clustered extinctions. While patterns of PD loss under different extinction scenarios are becoming well characterized in model phylogenies, analyses of real clades that often have unbalanced tree shapes remain scarce, particularly for marine organisms. Here, we use a fossil-calibrated phylogeny of all living scleractinian reef corals in conjunction with IUCN data on extinction vulnerabilities to quantify how loss of species in different threat categories will affect the PD of this group. Our analyses reveal that predicted PD loss in corals varies substantially among different threats, with extinctions due to bleaching and disease having the largest negative effects on PD. In general, more phylogenetically clustered extinctions lead to larger losses of PD in corals, but there are notable exceptions; extinction of rare corals from distantly-related old and unique lineages can also result in substantial PD loss. Thus our results show that loss of PD in reef corals is dependent on both tree shape and the nature of extinction threats.

The future of evolutionary diversity in reef corals

“…On the other hand, PD has been shown to poorly capture trait or functional diversity [19,103] especially on a regional scale [44,45]. More importantly, the most recent common ancestor of modern reef corals probably lived about 400 million years ago in the Palaeozoic [58], and many major coral lineages are relatively old [36]. Given their long history it is likely that some of the old lineages (e.g.…”

“…We used the supertree method modified from two recent studies [34,36] to reconstruct the phylogeny of the scleractinian clade, comprising 842 reef and 705 non-reef species [50]. The source trees were derived from a molecular phylogeny of 474 species (based on seven mitochondrial DNA markers), 13 morphological trees and a taxonomic tree [34,36].…”

“…Reductions in PD and PSV, as well as associated changes in tree shape, were compared with a null model of the same level of random species loss (1000 replicates) [36,43,44,73]. To quantify the declines in PD and PSV specifically, we computed the excess loss of each metric under the 'observed' scenario relative to random, as a percentage of the random result [74].…”

The evolution of fishes and corals on reefs: form, function and interdependence

“…We now have a deeper understanding of the changes in the location and extent of coral-bearing hardgrounds through time (Kiessling, 2009), the nature and extent of coral outcrops (Wilson & Rosen, 1998;Kiessling, Aberhan & Villier, 2008;Johnson et al, 2015;Wilson, 2015), and the origins of many coral growth forms within the Acroporidae, the family which numerically dominates modern coral reefs (Wallace & Rosen, 2006). This information has recently been supplemented by molecular phylogenies (Kerr, 2005;Fukami et al, 2008;Huang & Roy, 2013). These molecular trees have, for the first time, permitted a direct comparison of the evolutionary history of fishes and corals, using similar methods.…”

Fossils, phylogenies, and the challenge of preserving evolutionary history in the face of anthropogenic extinctions

“…In groups as varied as birds, mammals, and plants, studies have shown that extinctions of species currently on the International Union for the Conservation of Nature Red List of Threatened Species would lead to a much larger loss of EH than expected under randomly distributed extinction of the same number of species (4)(5)(6). This disproportionate loss of EH stems from phylogenetic clustering of anthropogenic extinctions (1) with a bias toward the loss of species-poor and geologically old taxa (7)(8)(9). Such predictions, along with the realization that not all species currently threatened by human activities can be saved, have motivated the development of various strategies for minimizing the loss of EH (8,10,11).…”