Single Ecological Shifts

 

Single ecological shifts that may impact phenotypic and lineage diversification range from catastrophic earth history events such as the the mass extinctions at the K-T boundary to the invasion of a new adaptive zone following a key innovation. These analyses require that we can identify a period in time or a particular branch on the phylogeny when the shift occurred, we can then estimate the rate of evolution (phenotypic or net diversification) before and after the event, or in clades with and without the innovation.

The association between diversification and evolutionary innovations has been well documented and tested in studies of taxonomic richness but the impact that such innovations have on the diversity of form and function is less well understood.  To address this question we investigated the impact of two design breakthroughs within the jaws of parrotfishes, the novel intramandibular joint and the modified pharyngeal apparatus.  We quantified morphological diversity within six functionally important oral jaw traits using the Brownian motion rate of evolution to correct for phylogenetic and time-related biases and compared these rates across clades that did and did-not possess the intramandibular joint and the parrotfish pharyngeal jaw. We found that no change in morphological diversity was associated with the pharyngeal jaw modification alone but rates of oral jaw diversification were up to 8x faster in parrotfish species that possessed both innovation.


Price, S.A., Wainwright, P.W., Bellwood, D. R, Kazancioglu, E., Collar, D. C. & Near, T.J. Functional innovation and morphological diversification in parrotfishes. 2010. Evolution 64(10), 3057-3068 (DOI 10.1111/1558-5646.2010.01036.x)

Functional innovations and morphological diversification in parrotfishes

Parrotfish pharyngeal jaw. UPJ upper pharyngeal jaw, LPJ lower pharyngeal jaw, EB4 4th epibranchial, Nc neurocranium and Di diarthrosis. Figure 2 from Price et al. 2010.

Modern whales have often been described as an adaptive radiation spurred either by key innovations or ecological opportunity following the demise of archaic whales. However, recent analyses of diversification rate shifts using molecular phylogenies have found no evidence of increased speciation rates during the early evolution of living whales. We repeated these analyses building a time-calibrated molecular phylogeny and in addition looked for the pattern of early ecological diversification which is also expected to accompany adaptive radiations. We used a data mining approach to gather a data from the literature on body length and diet and analysed it using disparity-through-time plot shown to the left and fitting various models of evolution.  We that show cetacean lineages partitioned size niches early in the evolutionary history of modern whales and that changes in size are consistent with shifts in dietary strategy. We conclude that the signature of adaptive radiations may be retained within morphological traits even after the signature of an early burst of diversification has been erased from the structure of the phylogeny. This study was in collaboration with Graham Slater, Francesco Santini & Mike Alfaro at UCLA.


I am currently working on extending this analysis by looking at the evolution of body size in fossil cetaceans using the supertree of extinct & extant cetaceans that I and my colleagues are constructing (see here). I am also working on the relationship between body size and reproductive strategy in modern cetaceans in comparison to terrestrial mammals.


Slater, G. J.*, Price, S. A.*, Santini, F. & Alfaro, M. E. 2010 Early

adaptive diversification in body size without rapid cladogenesis in

modern cetaceans. Proceedings of the Royal Society of London, B

277, 3097-3104 (DOI 10.1098/rspb.2010.0408). *joint 1st Authorship

Adaptive diversification of cetaceans

Mean subclade disparity through time for whale body size (black line) compared to the expectation under Brownian motion (dotted line). This shows there is lower than expected average subclade disparity in cetacean body size suggesting that size niches were partitioned early in the evolutionary history of modern whales. Figure 4 from Slater*, Price*, et al. 2010

Diversification of present-day mammals

Did the demise of the dinosaurs at the end of the Cretaceous trigger the diversification of present-day mammals? Using a virtually complete time-calibrated supertree of mammals we showed that net per-lineage diversification rates barely changed across the K-T boundary. Instead, rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago before falling and remaining low until accelerating again throughout the Eocene and Oligocene. This study was lead by Olaf Bininda-Emonds and was part of a large international collaboration looking at the phylogeny, extinction risk and life history of mammals headed by Andy Purivs, Georgina Mace & John Gittleman.


Bininida-Emonds, O.R.P., Cardillo, M., Jones, K.E., MacPhee,

R.D.E., Beck, R.M.D., Grenyer, R., Price, S.A., Vos, R., Gittleman,

J.L., Purvis, A. 2007. The delayed rise of present-day mammals.

Nature 446, 507-512.

Representation of a complete, time-calibrated phylogeny of mammals built using supertree methodology with the K-T event indicated by the dotted line. Figure 1 from Bininda-Emonds et al. 2007.