How Species Longevity, Intraspecific Morphological Variation, and Geographic Range Size Are Related: A Comparison Using Late Cambrian Trilobites

Abstract

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but itis also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall. K E Y W O R D S :Duration, evolutionary rates, morphological evolution, paleobiology, phylogenetic signal.

Phylogenetic signal in extinction selectivity in Devonian terebratulide brachiopods

“…This approach to time-scaling the phylogeny results in many zero-length internal branches (Bapst 2013). As has been commonly done in other molecular and morphological studies (e.g., Laurin et al 2009;Hopkins 2011), we add a small, arbitrary amount of time (0.01 Myr) to all zero-length branches in the terebratulide tree. We obtained radiometric ages of stage boundaries from the revised Devonian timescale of Ogg et al (2009).…”

“…Geographic range size can also be phylogenetically structured, with more closely related lineages exhibiting ranges that are more similar in size than expected by chance. This pattern of phylogenetic conservatism occurs in sister species (Taylor and Gotelli 1994) and putative ancestor-descendant pairs (Jablonski 1987;Hunt et al 2005) and larger clades Hopkins 2011), as well as across a diversity of distantly related groups including trilobites (Hopkins 2011), fish (Taylor and Gotelli 1994), mollusks (Jablonski 1987;Hunt et al 2005), and mammals . Presumably the phylogenetic pattern of range size conservatism reflects heritable aspects of life history (e.g., dispersal mode) and physiology (e.g., thermal tolerance) that give rise to the realized geographic distributions of taxa.…”

“…For example, short taxon durations were associated with small geographic range sizes (e.g., Harnik 2011) and narrow habitat tolerances (e.g., Kammer et al 1998) at times in the geologic past. Due to the real and/or perceived challenges of using morphological data gathered from fossil specimens to develop explicit phylogenetic hypotheses (e.g., because of limited numbers of morphological characters and homoplasy), most studies of extinction selectivity using the fossil record have ignored phylogenetic relationships (though see Carlson et al 2004;Smith and Roy 2006;Fitzgerald and Carlson 2007;Carlson and Fitzgerald 2008a;Friedman 2009;Crampton et al 2010;Green et al 2011;Hopkins 2011;Kolbe et al 2011). This omission inflates the degrees of freedom in statistical analyses, because taxa are assumed to be independent despite their shared evolutionary history (Felsenstein 1985;Harvey and Pagel 1991), and leaves open the possibility that observed associations are indirect, reflecting shared evolutionary history rather than the direct influence of particular biological traits on taxon durations and extinction rates.…”

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

“…Thus, existing studies do not readily allow direct comparisons of past losses of EH with those predicted for anthropogenic extinctions. Although temporal durations of species in the fossil record are more difficult to estimate reliably than those of higher taxa (23), a number of paleontological studies have used fossil species successfully to test important evolutionary and biogeographic hypotheses (21,(51)(52)(53)(54)(55)(56) as well as various aspects of the extinction process (57)(58)(59). With the increasing availability of large, taxonomically standardized paleontological databases, analyses of age selectivity of extinctions at the species level, such as the one undertaken here, are now feasible, especially on regional scales.…”

Intraspecific variation in fossil vertebrate populations: Fossil killifishes (Actinopterygii: Cyprinodontiformes) from the Oligocene of Central Europe

“…However, comparisons between variation in extinct and extant populations of invertebrates and vertebrates show that palaeontological samples were not strongly affected by time-averaging (Bell and Legendre, 1987;MacFadden, 1989;Bush et al, 2002;Hunt, 2004a, b). Studies of variation in extinct populations or species are more common when studying invertebrates, such as trilobites (Hughes and Labandeira, 1995;Labandeira and Hughes, 1994;Webster, 2007Webster, , 2014Hopkins, 2011), ammonoids (Hohenegger and Tatzreiter, 1992;Korn and Klug, 2007;Monnet et al, 2010;De Baets et al, 2013), and crinoids (Lane, 1963;Meyer and Ausich, 1997). Among fossil tetrapods, studies on intraspecific variation have been conducted for example for dinosaurs (Raath, 1990;Bever et al, 2011;Foth and Rauhut, 2013), ichthyosaurs (Maxwell, 2012), rodents (Renaud et al, 2006;Lazzari et al, 2010) and horses (MacFadden, 1997).…”