Going under down under? Lineage ages argue for extensive survival of the Oligocene marine transgression on Zealandia

Abstract

Twenty‐five years ago, it was suggested that current‐day New Zealand, part of the largely sunken continent of Zealandia, could have been completely inundated during the Oligocene marine transgression (OMT) some 25–23 million years ago. Such an event would, of necessity, imply that all terrestrial, freshwater, and maybe coastal marine species must have dispersed there since. This idea has generated heated debate, on which geological, palaeontological and molecular data are being brought to bear. Here, we review the phylogeographic literature in the form of molecular estimates of divergence times between New Zealand lineages and their closest overseas sister groups. Using an event‐based approach, we show that these divergence times follow approximately a smooth exponential over the last 50 Ma or more. Approximately 74 of these 248 lineages appear to have survived the OMT in situ; some of these major lineages comprise multiple additional lineages as a result of autochthonous speciation prior to the OMT. Non‐volant terrestrial animals, freshwater animals and trees are particularly well represented in surviving lineages, whereas marine animals, herbs and shrubs tend to show more recent arrival times. There is no evidence for a deficit of pre‐Oligocene lineages, nor an excess of ones arriving just afterwards. The pattern is one of geometric increase in new lineages with more recent time, reflecting a balance between immigration and extinction. Consequently, this large body of molecular data provides no evidence for complete inundation of New Zealand during the Oligocene. In conjunction with new geological and palaeontological findings, these data suggest that it is time to put the idea to rest.

Phylogenetic divergence of island biotas: Molecular dates, extinction, and “relict” lineages

“…Similar to the NZ findings of Wallis and Jorge (), the current study reveals smooth, relatively continuous divergence‐age distributions for two oceanic island biotas—assemblages that were unequivocally established by trans‐oceanic dispersal (Figure b,c). Below, we discuss potential reasons for the apparent absence of older lineage divergence “pulses” associated with early land emergence, and the presence of numerous island lineages that apparently pre‐date island formation.…”

“…We collated information from these publications on the estimated divergence date of Lord Howe and Chatham Islands lineages from their sister lineages. We followed Wallis and Jorge () in using the stem age divergence, rather than the crown radiation divergence, as in the majority of cases only a single lineage was sampled from each Island. Where different divergence dates were estimated using different genes (e.g., Heenan et al, ), we calculated an average divergence date across the genes (Table ).…”

“…We then fitted an exponential distribution to divergence times using the fitdist function of the fitdistrplus (Delignette‐Muller, Pouillot, Denis, & Dutang, ) package in r (R Core Team, ) to test for goodness of fit to an exponential distribution. Taxa for which no genetic differentiation was detected between island and mainland samples were excluded from the goodness of fit test, as these data may skew the distributions (Wallis & Jorge, ). It was hypothesized that there would be an excess of arrival times directly after the re‐emergence of the Chatham Islands ( ca .…”

Navigating the southern seas with small fins: Genetic connectivity of seahorses (Hippocampus abdominalis) across the Tasman Sea

“…Larval dispersal is thought to influence species interconnectedness in aquatic environments (Ayre, Hughes, & Standish, 1997), but the Bass Strait, Cook Strait, and Tasman Sea appear to form robust barriers to gene flow in many species with extended larval dispersal (e.g. In contrast, the Tasman Sea serves as only a partial barrier to gene flow in the small number of pelagic teleosts that have been studied in the region (Wallis & Jorge, 2018), and Coscinasterias sea stars that utilize rafting as a means of adult dispersal show a pattern of genetic structure almost identical to that of H. abdominalis (Waters & Roy, 2003a, 2003b. In contrast, the Tasman Sea serves as only a partial barrier to gene flow in the small number of pelagic teleosts that have been studied in the region (Wallis & Jorge, 2018), and Coscinasterias sea stars that utilize rafting as a means of adult dispersal show a pattern of genetic structure almost identical to that of H. abdominalis (Waters & Roy, 2003a, 2003b.…”

“…Because of the prominent eastward circulation of the major currents of the Tasman Sea, species dispersal is often presumed to have occurred from Australia to New Zealand, a phenomenon termed the WWD hypothesis (Waters, 2008). Cumming, Nikula, Spencer, & Waters, 2014;Cumming, Nikula, Spencer, & Waters, 2016;Fraser, Spencer, & Waters, 2009;Pfaller, Payton, Bjorndal, Bolten, & McDaniel, 2019;Wallis & Jorge, 2018), despite the fact K E Y W O R D S bipolar seesaw, dispersal, genetic connectivity, Hippocampus, marine biogeography, migration, rafting, southern hemisphere, Tasman Sea F I G U R E 1 Haplotype frequency distributions for each site are displayed on the map of southeastern Australia and New Zealand for 174 Hippocampus abdominalis specimens from ten localities: Adelaide (AD), Sydney (SY), Derwent Estuary (DE), Northwest Bay (NB), Raglan (RA), Tauranga (TA), Napier (NA), Wellington (WE), Christchurch (CC), and Stewart Island (SI). Cumming, Nikula, Spencer, & Waters, 2014;Cumming, Nikula, Spencer, & Waters, 2016;Fraser, Spencer, & Waters, 2009;Pfaller, Payton, Bjorndal, Bolten, & McDaniel, 2019;Wallis & Jorge, 2018), despite the fact K E Y W O R D S bipolar seesaw, dispersal, genetic connectivity, Hippocampus, marine biogeography, migration, rafting, southern hemisphere, Tasman Sea F I G U R E 1 Haplotype frequency distributions for each site are displayed on the map of southeastern Australia and New Zealand for 174 Hippocampus abdominalis specimens from ten localities: Adelaide (AD), Sydney (SY), Derwent Estuary (DE), Northwest Bay (NB), Raglan (RA), Tauranga (TA), Napier (NA), Wellington (WE), Christchurch (CC), and Stewart Island (SI).…”