Testing synchrony in historical biogeography: the case of new world primates and hystricognathi rodents

Abstract

The abrupt appearance of primates and hystricognath rodents in early Oligocene deposits of South America has puzzled mastozoologists for decades. Based on the geoclimatic changes that occurred during the Eocene/Oligocene transition period that may have favoured their dispersal, researchers have proposed the hypothesis that these groups arrived in synchrony. Nevertheless, the hypothesis of synchronous origins of platyrrhine and caviomorph in South America has not been explicitly evaluated. Our aim in this work was to apply a formal test for synchronous divergence times to the Platyrrhini and Caviomorpha splits. We have examined a previous work on platyrrhine and hystricognath origins, applied the test to a case where synchrony is known to occur and conducted simulations to show that it is possible to formally test the age of synchronous nodes. We show that the absolute ages of Platyrrhini/Catarrhini and Caviomorpha/Phiomorpha splits depend on data partitioning and that the test applied consistently detected synchronous events when they were known to have happened. The hypothesis that the arrival of primates and hystricognaths to the New World consisted of a unique event cannot be rejected.

Keywords: South America; biogeography; eocene; oligocene; relaxed molecular clock.

Figure 1

Timescale of New World Primates and Hystricognathi rodents evolution inferred using the P2006 data set under partitioned (black line) and concatenated (grey line) schemes. Note: Platyrrhini/Catarrhini and Caviomorpha/Phiomorpha splits are marked with stars.

Figure 2

Prior and posterior distribution of the difference D between the Platyrrhini/Catarrhini and Caviomorpha/Phiomorpha divergence times under partitioned (red) and concatenated (blue) data sets. Notes: Solid lines, posterior distributions; dashed lines, prior distributions.

Figure 3

Hox gene family phylogeny depicting the pairs of splits in which the differences between divergence times were computed. Each pair is numbered respectively. Grey circles show the duplication events.

Figure 4

Trees with branch lengths representing absolute times (A) and evolutionary rates (B) used to simulate the synchronous data set. In (A), note that the Platyrrhini/Catarrhini and Caviomorpha/Phiomorpha divergence times were forced to be synchronous (red branches). In (B), note the difference in evolutionary rates in Primates and Rodentia.

Figure 5

Boxplots of the posterior distributions of the difference between the eleven Hox gene pairs shown in Figure 3. The 95% HPD interval is depicted as the grey bar in each boxplot. Note: D = 0 is present in all HPD intervals.

Figure 6

Boxplots of the posterior distributions of the difference between the Platyrrhini/Catarrhini and Caviomorpha/Phiomorpha divergence times when synchrony was enforced. The empirical P2006 posterior distribution is depicted in the last red boxplot, identified by arrows, (A) concatenated data set; (B) partitioned data set.

Figure 7

Hlistograms is of the means of the posterior distributions of simulated data. The minimium and maximum values of the 95% HPD intervals are marked by the red dashed lines. Note: The empirical value is present within all HPD intervals (solid black line).