Biological Considerations of the Marsupial-Placental Dichotomy

Lillegraven, Jason A.

doi:10.2307/2407079

Cited by 103 publications

(105 citation statements)

References 14 publications

(18 reference statements)

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“…After birth, marsupial young begin an extended period of fixation onto a nipple. This both compromises the ability of the mother to forage in aquatic environments and provides an early developmental constraint on the evolution of an anteater-style ''beak'' (62). The only (remotely) ecologically analogous marsupials to the platypus and echidnas, the semiaquatic yapok and termite-eating numbat, are far more restricted in their aquatic and fossorial activities compared with their monotreme counterparts.…”

Section: Discussionmentioning

confidence: 99%

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

Phillips

Bennett

Lee

2009

Proc. Natl. Acad. Sci. U.S.A.

130

103

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The semiaquatic platypus and terrestrial echidnas (spiny anteaters) are the only living egg-laying mammals (monotremes). The fossil record has provided few clues as to their origins and the evolution of their ecological specializations; however, recent reassignment of the Early Cretaceous Teinolophos and Steropodon to the platypus lineage implies that platypuses and echidnas diverged >112.5 million years ago, reinforcing the notion of monotremes as living fossils. This placement is based primarily on characters related to a single feature, the enlarged mandibular canal, which supplies blood vessels and dense electrosensory receptors to the platypus bill. Our reevaluation of the morphological data instead groups platypus and echidnas to the exclusion of Teinolophos and Steropodon and suggests that an enlarged mandibular canal is ancestral for monotremes (partly reversed in echidnas, in association with general mandibular reduction). A multigene evaluation of the echidna-platypus divergence using both a relaxed molecular clock and direct fossil calibrations reveals a recent split of 19 -48 million years ago. Platypus-like monotremes (Monotrematum) predate this divergence, indicating that echidnas had aquatically foraging ancestors that reinvaded terrestrial ecosystems. This ecological shift and the associated radiation of echidnas represent a recent expansion of niche space despite potential competition from marsupials. Monotremes might have survived the invasion of marsupials into Australasia by exploiting ecological niches in which marsupials are restricted by their reproductive mode. Morphology, ecology, and molecular biology together indicate that Teinolophos and Steropodon are basal monotremes rather than platypus relatives, and that living monotremes are a relatively recent radiation.calibration ͉ molecular dating ͉ Monotremata ͉ niche ͉ phylogeny

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Section: Discussionmentioning

confidence: 99%

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

Phillips

Bennett

Lee

2009

Proc. Natl. Acad. Sci. U.S.A.

130

103

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“…Thus in general it appears that the tammar foetus is well protected from any deleterious immunological effects which might result from maternal sensitization to male histocompatibility antigens. However, this need not necessarily mean that the problem of foetal rejection has not played a part during marsupial evolution by preventing development of more extensive foeto-maternal contact during gestation as suggested by Moors (1974) and Lillegraven (1975).…”

Section: Discussionmentioning

confidence: 99%

“…Since the period of close foeto-maternal contact in marsupials is so short, it has been suggested (Tyndale-Biscoe 1973;Moors 1974;Lillegraven 1975) that marsupials may not have evolved mechanisms similar to those that protect the eutherian foetus from rejection and allow a prolonged intra-uterine development. If this is so, it seems possible that sensitization of the female to male histocompatibility antigens may adversely affect fertility in marsupials.…”

Section: Introductionmentioning

confidence: 99%

Immunological Aspects of Gestation in the Tammar Wallaby, Macropus eugenii

Walker¹,

Tyndale-Biscoe²

1978

Aust. Jnl. Of Bio. Sci.

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Sensitization to male histocompatibility antigens and repeated pregnancy to the same male were found to have little effect on fertility or length of gestation in the tammar wallaby, M. eugenii. However, in some sensitized females a long interval occurred between removal of pouch young and the next birth. In addition to studies on fertility, the immunological response of female tammars to their mate has been examined by one-way mixed leucocyte culture (MLC) carried out at the beginning and end of one breeding season. In virgin females, examined at the beginning of the breeding season, the MLC response to the prospective mate peaked on day 6. In contrast, by the end of the season, MLC responses were much lower and peaked earlier, on day 3 to day 5.

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“…The evolutionary origins of these differences, as well as the potential evolutionary constraints imposed by one or the other strategy have long been topics of broad interest and controversy (e.g., Tyndale-Biscoe, 1973;Lillegraven, 1975;Kirsch, 1977a,b;Lee and Cockburn, 1985;Lillegraven et al, 1987;Tyndale-Biscoe and Renfree, 1987;Hughes and Hall, 1988;Cockburn, 1989;Maier, 1993Maier, , 1999Sears, 2004;and references therein).…”

Section: Introductionmentioning

confidence: 99%

“…Several evolutionary scenarios have been presented to account for the differences between marsupials and eutherians. Some scenarios emphasize constraint, claiming that marsupials have been unable to develop suffi-ciently effective placentation methods or immunological protection of the fetus (e.g., Lillegraven, 1975;Lillegraven et al, 1987), while others argue that the marsupial mode of reproduction has evolved in response to distinct selective pressures and has significant advantages in some circumstances over the mode of reproduction seen in eutherians (e.g., Kirsch, 1977a,b;Parker, 1977;Hayssen et al, 1985). Others have claimed that marsupials and placentals represent ends of a continuum and that the reproductive strategies should not be seen as distinct alternatives, but merely differences in emphasis, perhaps the consequences of initial minor differences that have become magnified over time (e.g., Renfree, 1983Renfree, , 1995Tyndale-Biscoe and Renfree, 1987).…”

Section: Introductionmentioning

confidence: 99%

Craniofacial development in marsupial mammals: Developmental origins of evolutionary change

Smith

2006

Developmental Dynamics

102

119

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Biologists have long studied the evolutionary consequences of the differences in reproductive and life history strategies of marsupial and eutherian mammals. Over the past few decades, the impact of these strategies on the development of the marsupial embryo and neonate has received attention. In this review, the differences in development in the craniofacial region in marsupial and eutherian mammals will be discussed. The review will highlight differences at the organogenic and cellular levels, and discuss hypotheses for shifts in the expression of important regulatory genes. The major difference in the organogenic period is a whole-scale shift in the relative timing of central nervous system structures, in particular those of the forebrain, which are delayed in marsupials, relative to the structures of the oral-facial apparatus. Correlated with the delay in development of nervous system structures, the ossification of the bones of the neurocranium are delayed, while those of the face are accelerated. This study will also review work showing that the neural crest, which provides much of the cellular material to the facial skeleton and may also carry important patterning information, is notably accelerated in its development in marsupials. Potential consequences of these observations for hypotheses on constraint, evolutionary integration, and the existence of developmental modules is discussed. Finally, the implications of these results for hypotheses on the genetic modulation of craniofacial patterning are presented.

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Biological Considerations of the Marsupial-Placental Dichotomy

Cited by 103 publications

References 14 publications

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

Immunological Aspects of Gestation in the Tammar Wallaby, Macropus eugenii

Craniofacial development in marsupial mammals: Developmental origins of evolutionary change

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