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Functional ecological convergence between the thylacine and small prey-focused canids - PubMed

  • ️Fri Jan 01 2021

Functional ecological convergence between the thylacine and small prey-focused canids

Douglass S Rovinsky et al. BMC Ecol Evol. 2021.

Abstract

Background: Morphological convergence is a fundamental aspect of evolution, allowing for inference of the biology and ecology of extinct species by comparison with the form and function of living species as analogues. The thylacine (Thylacinus cynocephalus), the iconic recently extinct marsupial, is considered a classic example of convergent evolution with the distantly related placental wolf or dog, though almost nothing is actually known regarding its ecology. This lack of data leads to questions regarding the degree of convergence with, and the similarity of, the functional ecology of the thylacine and the wolf/dog. Here, we examined the cranium of the thylacine using 3D geometric morphometrics and two quantitative tests of convergence to more precisely determine convergent analogues, within a phylogenetically informed dataset of 56 comparative species across 12 families of marsupial and placental faunivorous mammals. Using this dataset, we investigated patterns of correlation between cranial shape and diet, phylogeny, and relative prey size across these terrestrial faunivores.

Results: We find a correlation between cranial, facial, and neurocranial shape and the ratio of prey-to-predator body mass, though neurocranial shape may not correlate with prey size within marsupials. The thylacine was found to group with predators that routinely take prey smaller than 45% of their own body mass, not with predators that take subequal-sized or larger prey. Both convergence tests find significant levels of convergence between the thylacine and the African jackals and South American 'foxes', with lesser support for the coyote and red fox. We find little support for convergence between the thylacine and the wolf or dog.

Conclusions: Our study finds little support for a wolf/dog-like functional ecology in the thylacine, with it instead being most similar to mid-sized canids such as African jackals and South American 'foxes' that mainly take prey less than half their size. This work suggests that concepts of convergence should extend beyond superficial similarity, and broader comparisons can lead to false interpretations of functional ecology. The thylacine was a predator of small to mid-sized prey, not a big-game specialist like the placental wolf.

Keywords: Convergent evolution; Feeding ecology; Functional ecology; Geometric morphometrics; Prey size; Tasmanian tiger; Thylacine.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1

The thylacine and canid comparatives. Photographs and crania in dorsal and lateral view of a, e thylacine (Thylacinus cynocephalus), b, f gray wolf (Canis lupus), c, g dingo, and d, h side-striped jackal (Lupulella adustus). Images not to scale. Image credits: a by E.J.K. Baker, Report of the Smithsonian Institution 1904, public domain, colourised by the authors; b by Neil Herbert, Yellowstone National Park, public domain; c by Jarrod Amoore CC BY 2.0; d by T.A. Hermann, NBII WikiCommons, public domain. Images have been adjusted to enhance contrast between subject and background by the authors. Crania e–h are mean shape mesh warps derived from this study’s dataset

Fig. 2
Fig. 2

Phylomorphospace of species mean cranial shape for 57 faunivorous mammals. Shape extremes of PC1 and PC2 generated by thin-plate spline warping of the mean skull mesh configuration. Tree root is indicated by open grey node, branches leading to species found to be significantly convergent with the thylacine in the total cranial dataset indicated in magenta and tips circled in black. The convergent species closest to the thylacine in morphospace, Lupulella adustus, is labelled

Fig. 3
Fig. 3

Phylomorphospace of a species mean facial shape and b neurocranial shape for 57 faunivorous mammals. Tree root is indicated by open grey node, and branches leading to species found to be significantly convergent with the thylacine in each respective dataset (facial or neurocranial) are indicated in magenta and tips circled in black

Fig. 4
Fig. 4

Mean cranial shape of large- and small-prey predators. a Large-prey (> 45% of predator body mass) mean shape and b small-prey (< 45% of predator mass) mean shape cranial meshes were generated by thin-plate spline warping of the mean cranial shape. Euclidean distances between the meshes of the c large-prey and d small-prey mean shapes and the total mean cranium shape are shown as deviation from the mean shape expressed by colour (blue–white–red). Blues show constriction relative to the mean shape, reds show expansion, with white as approximately congruent to the mean shape

Fig. 5
Fig. 5

Discrimination of prey size in the thylacine. Canonical Variates Analysis (CVA) discrimination scores of preferred prey size (> 45% or < 45% of predator body mass) within the a total cranial, b facial, and c neurocranial datasets. Group assignment of the thylacine listed to the right of each respective plot, along with the posterior probability (post. prob.) of the assignment

Fig. 6
Fig. 6

Candidate convergent species cluster phenogram. Unweighted Pair Group Method with Arithmetic mean (UPGMA) phenetic cluster analysis on the PC scores accounting for > 1% variance within the total cranial dataset. This group of species forms the candidate species input for all convergence analyses. The thylacine and the phenetic candidate group are called out in colour

Fig. 7
Fig. 7

Comparison of cranial shape between the thylacine, wolf, and maximally convergent species group. a Gray wolf (Canis lupus) mean cranial shape and b maximally convergent group (Chrysocyon brachyurus, Lupulella adustus, Lu. mesomelas, Lycalopex gymnocercus) mean cranial shape, with the Euclidean distances from the c mean thylacine shape shown by colour (blue–white–red), as in Fig. 4 above

Fig. 8
Fig. 8

Time-scaled phylogeny of faunivorous mammals used in this study. Assembled using topologies and divergence dates from recent studies (see Additional file 1: Table S7)

Fig. 9
Fig. 9

Landmark and semilandmark template. Template created on the approximately mean shape cranium of Cuon alpinus (dhole), shown in a lateral, b dorsal, and c ventral views. For definitions and detailed protocol, see Additional file 1: Table S8

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