Integrating biogeography, threat and evolutionary data to explore extinction crisis in the taxonomic group of cycads.

Kowiyou Yessoufou,Barnabas H Daru,Hosam O Elansary,Isaac Rampedi,Respinah Tafirei

doi:10.1002/ece3.2660

Abstract

Will the ongoing extinction crisis cause a severe loss of evolutionary information accumulated over millions of years on the tree of life? This question has been largely explored, particularly for vertebrates and angiosperms. However, no equivalent effort has been devoted to gymnosperms. Here, we address this question focusing on cycads, the gymnosperm group exhibiting the highest proportion of threatened species in the plant kingdom. We assembled the first complete phylogeny of cycads and assessed how species loss under three scenarios would impact the cycad tree of life. These scenarios are as follows: (1) All top 50% of evolutionarily distinct (ED) species are lost; (2) all threatened species are lost; and (3) only all threatened species in each IUCN category are lost. Finally, we analyzed the biogeographical pattern of cycad diversity hotspots and tested for gaps in the current global conservation network. First, we showed that threatened species are not significantly clustered on the cycad tree of life. Second, we showed that the loss of all vulnerable or endangered species does not depart significantly from random loss. In contrast, the loss of all top 50% ED, all threatened or all critically endangered species, would result in a greater loss of PD (Phylogenetic Diversity) than expected. To inform conservation decisions, we defined five hotpots of diversity, and depending on the diversity metric used, these hotspots are located in Southern Africa, Australia, Indo‐Pacific, and Mexico and all are found within protected areas. We conclude that the phylogenetic diversity accumulated over millions of years in the cycad tree of life would not survive the current extinction crisis. As such, prioritizing efforts based on ED and concentrating efforts on critically endangered species particularly in southern Africa, Australia, Indo‐Pacific, and Mexico are required to safeguarding the evolutionary diversity in the cycad tree of life.

Highlights

Originated ~300 million years ago (Hendricks, 1987), cycads are a fascinating plant group sharing morphological characteristics of ferns and angiosperms (Brenner, Stevenson, & Twigg, 2003; Norstog & Nicholls, 1997)
As the susceptibility of species to extinction is linked to their past evolutionary history (Davies et al, 2011; Vamosi & Wilson, 2008), reconstructing the tree of life of a particular taxonomic group is likely to inform, our understanding of the pattern of extinction risk in the group (Davies et al, 2011; Purvis, Agapow, Gittleman, & Mace, 2000), and how the tree of life could be pruned by species loss (Davies & Yessoufou, 2013; Mooers, Gascuel, Stadler, Li, & Steel, 2012; Parhar & Mooers, 2011; Purvis et al, 2000)
The emerging pattern in extinction risk studies indicates that threatened species are clustered on a phylogeny (Purvis et al, 2000; Yessoufou & Davies, 2016), and their loss would prune severely the branches of the tree of life (Davies, 2015)

Summary

| INTRODUCTION

Originated ~300 million years ago (Hendricks, 1987), cycads are a fascinating plant group sharing morphological characteristics of ferns and angiosperms (Brenner, Stevenson, & Twigg, 2003; Norstog & Nicholls, 1997). ED can capture broadly the biology of a particular group (Redding, DeWolff, & Mooers, 2010), and lastly, the preservation of high-E D species may lead to the preservation of uniquely divergent genomes (Warren et al, 2008) All these studies that address explicitly the preservation of the evolutionary diversity or employ an integrative approach to inform conservation, focus on vertebrates (Jetz et al, 2014; Redding et al, 2010) and increasingly on angiosperms (Daru & le Roux, 2016; Daru et al, 2015; Vamosi & Wilson, 2008) with no equivalent efforts ever made on gymnosperms, the latter has a unique evolutionary h istory in plant kingdom (Nagalingum et al, 2011). We contrast hotspots of multiple diversity facets of cycads across biogeographical regions and assess how well the current global protected area network preserves cycad diversity hotspots and cycad species that need urgent attention

| MATERIALS AND METHODS

Findings

| DISCUSSION

| CONCLUSION