Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa

Abstract

New Zealand's extinct flightless moa radiated rapidly into a large number of morphologically diverse species, which produced an equally large range of egg morphologies. The exact number of moa species, as well as the characteristics of the eggs they laid, remains contentious. Moreover, like most extinct species, we understand little about their nesting and incubation habits. We used a modified ancient DNA extraction procedure to recover exogenous mitochondrial and nuclear DNA from the inside and outside surfaces of moa eggs. We used sequences from the inside of 69 eggshells to directly assign these remains to seven of the 10 currently recognized moa species. In addition we were able to assign, to the species level, six of the rare reconstructed "whole" eggs. These molecular results enabled us to identify two distinct lineages within the genus Euryapteryx. Members of these lineages differed in eggshell thickness, with one lineage being characterized by a relatively thin eggshell. Unexpectedly, several thin-shelled eggs were also shown to belong to the heaviest moa of the genera Dinornis, Euryapteryx and Emeus, making these, to our knowledge, the most fragile of all avian eggs measured to date. Moreover, sex-specific DNA recovered from the outer surfaces of eggshells belonging to species of Dinornis and Euryapteryx suggest that these very thin eggs were likely to have been incubated by the lighter males. The thin nature of the eggshells of these larger species of moa, even if incubated by the male, suggests that egg breakage in these species would have been common if the typical contact method of avian egg incubation was used.avian eggs | exogenous DNA | endogenous DNA | ratite | evolution N ew Zealand's extinct moa (Aves: Dinornithiformes) were ratite birds. Living species of ratites include the emu and cassowary of Australia and New Guinea, the kiwi of New Zealand, and the rhea of South America. Extinct members include the elephant bird of Madagascar as well as approximately 10 species of moa (1-4). Moa were flightless and were particularly diverse in both size and in morphology (1, 2, 4-8). For example, members of the genus Dinornis were characterized by large body size, weighing as much as 250 kg, with extreme sexual dimorphism in which females were approximately twice the size of males (2, 5). In contrast, individuals of the coastal moa Euryapteryx curtus weighed as little as 9 kg (4) and females were approximately 20% larger than males. As a group, moa represented one of the most dramatic examples of morphological radiation in the history of vertebrates (1, 2, 6) and have been of international interest since originally described by Richard Owen in 1839 (9). This remarkable ratite group vanished soon after the settlement of New Zealand by Polynesians late in the 13th century (8, 10).Many questions about moa biology and evolution remain, despite more than 100 y of scientific investigation. Moa eggs ranged from 10 times the volume of a standard chicken egg (approximately 120 mm × 95 mm; ∼0.06 kg) to more than 8...

Twenty-first century advances in knowledge of the biology of moa (Aves: Dinornithiformes): a new morphological analysis and moa diagnoses revised

“…Thus thickness was shown to be a poor discriminator of taxa. Oskam et al (2011) noted that their data did not support two clades of Euryapteryx as suggested by Huynen et al (2010).…”

“…Therefore, it would be expected that Euryapteryx shell from Oamaru, South Island, would be on average thicker than shell from the Far North (northern North Island) in the one taxon. This expectation is met to an extent, with the thinner shell, all that B1.0 mm, being from the Far North; however, Huynen et al (2010): supplementary information) found that some of the thick shell was derived from the Far North (Tokerau Beach, Matai Bay and North Cape).…”

“…Given that the scale of the change in mean size of late Holocene individuals over the length of North Island (Northland to the Wairarapa) likely involves a doubling of weight, and that average size of Euryapteryx individuals further increases markedly in the South Island (Worthy 1987;, eggs of this species probably more than double in size from the Far North to Otago. This is exemplified by comparison of the size of Euryapteryx eggs from Tokerau Beach (Gill 2006) and that from Otago shown by Huynen et al (2010): Fig. 3A).…”

“…In a second paper, Huynen et al (2010) identified species and sex from exogenous mitochondrial (hypervariable region I) and nuclear DNA (sex specific markers) from both the inside and outside of the same fragments of pieces of moa eggshell. The authors were able to assign to species six of the 'complete' eggs, and shell fragments to seven of the 10 currently recognised species: Anomalopteryx didiformis; Megalapteryx didinus; Emeus crassus; Pachyornis geranoides; both Dinornis species; and Euryapteryx curtus.…”

Ancient DNA microsatellite analyses of the extinct New Zealand giant moa (Dinornis robustus) identify relatives within a single fossil site

“…From the observation of an even sex ratio among juvenile moa of the taxon Euryapteryx curtus (Allentoft et al, 2010), but not among the adults, a higher mortality among males has also been suggested. Incubation by males has been suggested by Huynen et al (2010) who identified putative moa male DNA on the surface of their eggshell.…”