Pattern and timing of diversification in Yucca (Agavaceae): specialized pollination does not escalate rates of diversification

Abstract

The yucca-yucca moth interaction is one of the most well-known and remarkable obligate pollination mutualisms, and is an important study system for understanding coevolution. Previous research suggests that specialist pollinators can promote rapid diversification in plants, and theoretical work has predicted that obligate pollination mutualism promotes cospeciation between plants and their pollinators, resulting in contemporaneous, parallel diversification. However, a lack of information about the age of Yucca has impeded efforts to test these hypotheses. We used analyses of 4322 AFLP markers and cpDNA sequence data representing six non-protein-coding regions (trnT-trnL, trnL, trnL intron, trnL-trnF, rps16 and clpP intron 2) from all 34 species to recover a consensus organismal phylogeny, and used penalized likelihood to estimate divergence times and speciation rates in Yucca. The results indicate that the pollination mutualism did not accelerate diversification, as Yucca diversity (34 species) is not significantly greater than that of its non-moth-pollinated sister group, Agave sensu latissimus (240 species). The new phylogenetic estimates also corroborate the suggestion that the plant-moth pollination mutualism has at least two origins within the Agavaceae. Finally, age estimates show significant discord between the age of Yucca (ca 6-10 Myr) and the current best estimates for the age of their pollinators (32-40 Myr).

Repeated independent evolution of obligate pollination mutualism in the Phyllantheae– Epicephala association

“…Kawakita & M. Kato 423 yucca systems have indicated that these associations arose only once in each partner lineage 40-60 Myr ago (Pellmyr & Leebens-Mack 1999;Rønsted et al 2005). An exception is Hesperoyucca whipplei, which is phylogenetically distant from the rest of the yuccas and independently established the mutualism with a yucca moth (Bogler et al 1995;Pellmyr et al 2007;Smith et al 2008). In the Phyllantheae-Epicephala system, major lineages of Phyllantheae had already emerged when Epicephala colonized these plants ca 30 Myr ago.…”

Host-associated divergence and incipient speciation in the yucca moth Prodoxus coloradensis (Lepidoptera: Prodoxidae) on three species of host plants

“…However, the development of highly polymorphic nucDNA microsatellite markers in the closely related genus Tegeticula (Drummond et al, 2009) provides new molecular methods for dissecting the finescale population dynamics of prodoxid yucca moths distributed among sympatric or parapatric host plants. Likewise, coordinated estimates of the phylogenetic relationships among Yucca (Pellmyr et al, 2007;Smith et al, 2008b) have created an expanded framework for evaluating the biogeographical history and diversification of these taxa with respect to host plant specialization. Coupled with these tools, coalescent models for multilocus phylogenetic inference (Edwards et al, 2007;Liu et al, 2008;Kubatko et al, 2009) and extensions of the basic isolation-with-migration coalescent model to multiple populations offer novel opportunities to examine the extent to which host specificity influences the divergence of phytophagous insects.…”

“…Within Prodoxus, stalk feeding is the most common mode of host plant use, from which a more limited number of fruit or leaffeeding taxa have evolved . Although obligate mutualisms are expected to promote coevolutionary divergence in both yuccas and yucca moths (Pellmyr and Krenn, 2002;Pellmyr and Segraves, 2003;Pellmyr, 1998, 2004;Althoff et al, 2006;Smith et al 2008a; but see Smith et al 2008b), the extent to which commensalist host specialization might lead to divergence among non-pollinating yucca moths is less clear. In the best-studied example to date, Prodoxus quinquepunctellus and Prodoxus decipiens have been shown to exhibit rapid phenological and morphological divergence among populations on different host species, particularly the evolution of ovipositor shape, a feature that is critical for successful oviposition and reproduction of yucca moths (Groman and Pellmyr, 2000;Althoff et al, 2001;Althoff and Pellmyr, 2002;Svensson et al, 2005).…”

Consideraciones taxonómicas de Yucca queretaroensis Piña (Agavaceae), una especie endémica del Semidesierto Queretano-Hidalguense

“…Pellmyr et al (2007) estudiaron las relaciones filogenéticas del género Yucca usando marcadores moleculares AFLP (polimorfismos en la longitud de fragmentos amplificados); en su análisis Y. queretaroensis se encuentra en la base de las tres secciones del género y Y. linearifolia permanece dentro de la sección Yucca. Smith et al (2008) muestran la posición de Y. queretaroensis en dos formas diferentes. La filogenia con base en marcadores AFLP la sitúa dentro de un grupo basal, hermano de todas las otras especies de Yucca; los autores indican que se trata de un resultado débilmente apoyado ya que los análisis no fueron consistentes.…”