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Different populations of a host species subject to variable patterns of selection due to cuckoo parasitism provide an optimal situation for studying natural selection and coevolution in action. We compared egg appearance and egg-rejection behavior of 2 common cuckoo (Cuculus canorus) hosts, the ashy-throated parrotbill (Paradoxornis alphonsianus) and the vinous-throated parrotbill (Paradoxornis webbianus) between mainland China and Taiwan population that have been segregated for 2-3 million years. Avian visual modeling showed that the mainland host population under strong selection from brood parasitism has evolved polymorphic eggs, while the island host population released from brood parasitism has maintained the original monomorphic egg phenotype. Furthermore, experiments indicated that under such long historical segregation, egg rejection in the island population decayed dramatically in the absence of cuckoo parasitism. This study provides strong evidence that egg-rejection ability can be dramatically deficient in host populations without brood parasitism compared to parasitized ones. The results further enhance our understanding of changes in eggrejection behavior in birds without the selection pressure of brood parasitism for an extended period of time. [ABSTRACT FROM AUTHOR]

BACKGROUND: All-trans retinoic acid (RA), the oxidative metabolite of vitamin A, is essential for normal development. In addition, high levels of RA are teratogenic in many species. We have previously shown that excess RA results in immediate effects on the preimplantation embryo and on blastocyst development. This study was conducted to clarify the long-term survival of mouse blastocyst and the effect of RA on gene expression. METHODS AND RESULTS: Using an in vitro model, we identified the immediate adverse impact of RA on mouse blastocyst development. This involved an inhibition of cell proliferation and growth retardation. Using an in vivo model, we also identified the resorption of postimplanted blastocysts that had been treated with excess RA. Analysis of RA-mediated gene induction was also included. The retinoic acid receptors RARα and RARγ were constitutively expressed in the blastocyst and the inner cell mass, whereas RARβ was induced upon RA treatment. CONCLUSIONS: This is the first evidence to show the impacts of RA on mouse blastocysts in vitro and any carry-over effects in the uterus. There is a retardation of early postimplantation blastocyst development and then subsequent blastocyst death. Our findings also show that there is some degree of selective induction of retinoic acid receptors when excess RA is administered to the blastocysts. [ABSTRACT FROM AUTHOR]