1981/02/01 by Ted N. Pettit, G. Causey Whittow, G. C. Whittow · 2 citations
Environmental Science · Agricultural and Biological Sciences · #Avian ecology and behavior #Livestock and Poultry Management #Marine and fisheries research
paper · doi:10.2307/1367615
During a study of embryonic respiration in the Wedgetailed Shearwater (Puffinus pacificus), an egg was collected and found to contain an embryonic duplicitas: a double monster or Siamese twin. This egg was collected on 7 August 1979 from Manana Island, Oahu, Hawaii and was 40 + 1 days old; the incubation period for this species averages 52 days. After respiratory data had been obtained, the egg was dissected and a double-monster embryo was found inside. The body of the embryo was completely duplicated except for a common head with one eye absent and the brain exposed on the left side. This embryo conformed to Ulshafer and Clavert's (J. Embryol. Exp. Morphol. 53:237-243, 1979) Group I classification of avian double monsters. The yolk-free mass of the abnormal embryo (10.3 g) equalled 47% of the yolk-free mass of normally developed shearwater embryos of the same age. The incidence of malformation in Wedge-tailed Shearwaters is difficult to assess but in 170 eggs we have examined over a three-year period, this is the first embryonic anomaly found. This would place the incidence of malformation at 0.59%. Romanoff (Pathogenesis of the avian embryo, John Wiley and Sons, 1972) reported values of 0.8% to 0.06% for embryonic duplicitas in chicken eggs. In ducks the phenomenon is more common: about 2% of all fertilized eggs form double monsters. The effect is believed to be caused by changes in orientation of the egg within the shell gland during the critical period of symmetrization, resulting in the formation of two organizing centers (Ulshafer and Clavert 1979). Other teratogenic factors may include high levels of pesticides and mercury. Fisher (Pac. Sci. 27:220-225, 1973) reported high levels of toxic substances in the Laysan Albatross (Diomedea immutabilis) on Midway Atoll but we know of no such stu ies on other procellariiform birds. This study was supported in part by the National Science Foundation (Grant #PCM-12351-AO1 to G. Caus y Whittow) and the Leahi Trust Fund, Research Corporation of the University of Hawaii (Grant #1979 to Ted N. Pettit).