Identifying Anagenesis and Cladogenesis in the Fossil Record

LETTER LETTER

Identifying anagenesis and cladogenesis in the fossil record

Strotz and Allen (1) examined our recently ary lineage phylogeny. Under their method- Tracy Azea,1,ThomasH.G.Ezardb, published phylogeny of Cenozoic macroper- ology, Strotz and Allen (1) must infer clado- Andy Purvisc, Helen K. Coxalld, forate planktonic foraminifera (2) to assess genesis for this biostratigraphic split due to Duncan R. M. Stewarte,BridgetS. the relative frequency of anagenesis (evolu- the substantial range overlap of these mor- Wade f, and Paul N. Pearsona tion within a single evolving lineage) and phospecies (∼12 My). However, experiments aSchool of Earth and Ocean Sciences, Cardiff cladogenesis (lineage branching) in the pro- have shown that these morphs are ecotypic University, Cardiff CF10 3AT, United duction of new morphospecies. They con- variants of a single lineage that are related to Kingdom; bCentre for Biological Sciences, clude that anagenesis is much less prevalent food supply and other environmental varia- University of Southampton, Southampton than indicated in our phylogeny. bles (3), a hypothesis that is also supported by SO17 1BJ, United Kingdom; cDepartment of We disagree with the authors’ criteria for genetic analysis (4). Life Sciences, Imperial College London, distinguishing anagenesis from cladogenesis Strotz and Allen (1) allow fossil morpho- in the fossil record, which is based on the as- species to belong to the same lineage as long Berkshire SL5 7PY, United Kingdom; d sumption that “morphospecies that coexist as they do not coexist for more than 0.6 My Department of Geological Sciences, Stockholm temporally are reproductively isolated, and in the Neogene or 2.4 My for the Paleogene. University, SE-106 91 Stockholm, Sweden; therefore independently evolving.” This These ﬁgures are entirely arbitrary, seemingly eFort Halstead, Kent TN14 7BP, United forces Strotz and Allen to interpret as sepa- drawn from just two studies of evolutionary Kingdom; and fDepartment of Earth Sciences, rate, cladogenetically produced entities (i)all rates within lineages that are not representa- University College London, London WC1E extant morphospecies and (ii)allfossilmor- tive of the group as a whole. 6BT, United Kingdom phospecies with a substantial overlap in their We support the integration of fossil and stratigraphic ranges. Here we show why nei- molecular data as the most robust method

ther interpretation is safe. for determining the phylogenetic history of a 1 Strotz LC, Allen AP (2013) Assessing the role of cladogenesis in Historically, planktonic foraminifera have group, but we deliberately avoided genetic macroevolution by integrating fossil and molecular evidence. Proc been widely used for biostratigraphic re- evidence in constructing our fossil phylogeny Natl Acad Sci USA 110(8):2904–2909. 2 Aze T, et al. (2011) A phylogeny of Cenozoic macroperforate search; as a result, morphologically inter- so that it could be considered independent. planktonic foraminifera from fossil data. Biol Rev Camb Philos Soc grading populations have been subject to We acknowledged that many more speciation 86(4):900–927. considerable taxonomic splitting to better events might have occurred than are resolved 3 Bijma JC, Hemleben C, Oberhänsli H, Spindler M (1992) The effects of increased water fertility on tropical spinose planktonic foraminifers subdivide geological time (2). The range over- in our phylogeny. Strotz and Allen (1) claim in laboratory cultures. J Foraminiferal Res 22(3):242–256. lap of many morphospecies is an artifact of to have integrated molecular data with the 4 André A, et al. (2012) The cryptic and the apparent reversed: Lack ﬁ of genetic differentiation within the morphologically diverse plexus the typological approach used for de ning fossil data we presented (2); however, there of the planktonic foraminifer Globigerinoides sacculifer. Paleobiol species in the geological record and does is no description in their methods section of 39(1):21–39. not necessarily imply cladogenesis. how this was done. 5 Pearson PN, Olsson RK, Huber BT, Hemleben C, Berggren WA (eds) (2006) Atlas of Eocene Planktonic Foraminifera (Cushman Consider one of the most abundant extant In summary, Strotz and Allen (1) conclude Foundation for Foraminiferal Research, Fredericksburg, VA), Vol. 41. species, Globigerinoides sacculifer sensu lato. what they assume: that the names given by This species has four commonly recognized biostratigraphers to morphospecies generally synonyms: quadrilobatus, trilobus, sacculifer, refer to genetically and evolutionarily sepa- Author contributions: T.A., T.H.G.E., A.P., H.K.C., D.R.M.S., B.S.W., and immaturus. We conservatively recognize rate entities, despite the statements of biostra- and P.N.P. wrote the paper. only trilobus and sacculifer in our morpho- tigraphers to the contrary both in the primary The authors declare no conﬂict of interest. species phylogeny and unite these morphs literature (5) and in our own description of 1To whom correspondence should be addressed. E-mail: azetl@cf. into a single lineage in our derived evolution- our methods (2). ac.uk.

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