The ecology of visual pigment tuning in an Australian marsupial: the honey possum Tarsipes rostratus

While most mammals have no more than two types of cone photoreceptor, four species of Australian marsupial have recently been shown to possess three types, and thus have the potential for trichromatic colour vision. Interestingly, the long-wave cones of the honey possum Tarsipes rostratus are tuned to longer wavelengths than those of the other species measured to date. We tested whether the honey possum's long-wave tuning is adaptive for visual tasks associated with its almost unique diet of nectar and pollen. We modelled three tasks: (1) detecting food-rich `target' flowers against their natural background of foliage or other vegetation; (2) discriminating target flowers from flowers of non-target species; (3) discerning the maturity of the most important target flowers. Initial comparisons of trichromacy vs dichromacy generally favoured the former, but interestingly dichromacy was no disadvantage in some cases. For tuning, we found that overall the honey possum's long-wave tuning is more adaptive than that of the other marsupial species. Nevertheless, the optimal tuning for tasks 1 and 2 would be at longer wavelengths still, implying that a different pressure or constraint operates against a further long-wave shift of the honey possum's L cone tuning. Our data show that a possible ecological pressure may be provided by the third task - the difficult and potentially critical discrimination of the maturity of the animal's major food supply, the flowers of Banksia attenuata

Trichromacy in Australian marsupials

Vertebrate color vision is best developed in fish, reptiles, and birds with four distinct cone receptor visual pigments [1, 2]. These pigments, providing sensitivity from ultraviolet to infrared light, are thought to have been present in ancestral vertebrates [3]. When placental mammals adopted nocturnality, they lost two visual pigments, reducing them to dichromacy; primates subsequently reevolved trichromacy [4]. Studies of mammalian color vision have largely overlooked marsupials despite the wide variety of species and ecological niches and, most importantly, their retention of reptilian retinal features such as oil droplets and double cones [5]. Using microspectrophotometry (MSP), we have investigated the spectral sensitivity of the photoreceptors of two Australian marsupials, the crepuscular, nectivorous honey possum (Tarsipes rostratus) and the arhythmic, insectivorous fat-tailed dunnart (Sminthopsis crassicaudata); these species are representatives of the two major taxonomic divisions of marsupials, the diprotodonts and polyprotodonts, respectively. Here, we report the presence of three spectrally distinct cone photoreceptor types in both species. It is the first evidence for the basis of trichromatic color vision in mammals other than primates. We suggest that Australian marsupials have retained an ancestral visual pigment that has been lost from placental mammals

Functional topography and integration of the contralateral and ipsilateral retinocollicular projections of ephrin-A-/- mice.

Topographically ordered projections are established by molecular guidance cues and refined by neuronal activity. Retinal input to a primary visual center, the superior colliculus (SC), is bilateral with a dense contralateral projection and a sparse ipsilateral one. Both projections are topographically organized, but in opposing anterior-posterior orientations. This arrangement provides functionally coherent input to each colliculus from the binocular visual field, supporting visual function. When guidance cues involved in contralateral topography (ephrin-As) are absent, crossed retinal ganglion cell (RGC) axons form inappropriate terminations within the SC. However, the organization of the ipsilateral projection relative to the abnormal contralateral input remains unknown, as does the functional capacity of both projections. We show here that in ephrin-A(-/-) mice, the SC contains an expanded, diffuse ipsilateral projection. Electrophysiological recording demonstrated that topography of visually evoked responses recorded from the contralateral superior colliculus of ephrin-A(-/-) mice displayed similar functional disorder in all genotypes, contrasting with their different degrees of anatomical disorder. In contrast, ipsilateral responses were retinotopic in ephrin-A2(-/-) but disorganized in ephrin-A2/A5(-/-) mice. The lack of integration of binocular input resulted in specific visual deficits, which could be reversed by occlusion of one eye. The discrepancy between anatomical and functional topography in both the ipsilateral and contralateral projections implies suppression of inappropriately located terminals. Moreover, the misalignment of ipsilateral and contralateral visual information in ephrin-A2/A5(-/-) mice suggests a role for ephrin-As in integrating convergent visual inputs

Cone topography and spectral sensitivity in two potentially trichromatic marsupials, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus)

The potential for trichromacy in mammals, thought to be unique to primates, was recently discovered in two Australian marsupials. Whether the presence of three cone types, sensitive to short- (SWS), medium- (MWS) and long- (LWS) wavelengths, occurs across all marsupials remains unknown. Here, we have investigated the presence, distribution and spectral sensitivity of cone types in two further species, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus). Immunohistochemistry revealed that SWS cones in the quokka are concentrated in dorso-temporal retina, while in the quenda, two peaks were identified in naso-ventral and dorso-temporal retina. In both species, MWS/LWS cone spatial distributions matched those of retinal ganglion cells. Microspectrophotometry (MSP) confirmed that MWS and LWS cones are spectrally distinct, with mean wavelengths of maximum absorbance at 502 and 538 nm in the quokka, and at 509 and 551 nm, in the quenda. Although small SWS cone outer segments precluded MSP measurements, molecular analysis identified substitutions at key sites, accounting for a spectral shift from ultraviolet in the quenda to violet in the quokka. The presence of three cone types, along with previous findings in the fat-tailed dunnart and honey possum, suggests that three spectrally distinct cone types are a feature spanning the marsupials

The elements of success in a comprehensive state-wide program to safely reduce the rate of preterm birth.

BACKGROUND:In 2014, a whole-of-population and multi-faceted preterm birth prevention program was introduced in Western Australia with the single aim of safely lowering the rate of preterm birth. The program included new clinical guidelines, print and social media, and a dedicated new clinic. In the first full calendar year the rate of preterm birth fell by 7.6% and the reduction extended from the 28-31 week gestational age group upwards. OBJECTIVE:The objective of this study was to evaluate outcomes in greater depth and to also include the first three years of the program. STUDY DESIGN:This was a prospective population-based cohort study of perinatal outcomes in singleton pregnancies before and after commencement of the program. RESULTS:There was a significant reduction in preterm birth in the tertiary center which extended from 28 weeks gestation onwards and was ongoing. In non-tertiary centers there was an initial reduction, but this was not sustained past the first year. The greatest reduction was observed in pregnancies classified at first attendance as low risk. No benefit was observed in the private sector, but a significant reduction was seen in the remote region of the Kimberley where the program was first launched and vaginal progesterone had been made free-of-charge. CONCLUSION:Preterm birth rates can be safely reduced by a multi-faceted and whole-of-population program but the effectiveness requires continuing effort and will be greatest where the strategies are most targeted

Strategies to prevent preterm birth

After several decades of research, we now have evidence that at least six interventions are suitable for immediate use in contemporary clinical practice within high-resource settings and can be expected to safely reduce the rate of preterm birth. These interventions involve strategies to prevent non-medically indicated late preterm birth; use of maternal progesterone supplementation; surgical closure of the cervix with cerclage; prevention of exposure of pregnant women to cigarette smoke; judicious use of fertility treatments; and dedicated preterm birth prevention clinics. Quantification of the extent of success is difficult to predict and will be dependent on other clinical, cultural, societal, and economic factors operating in each environment. Further success can be anticipated in the coming years as other research discoveries are translated into clinical practice, including new approaches to treating intra-uterine infection, improvements in maternal nutrition, and lifestyle modifications to ameliorate maternal stress. The widespread use of human papillomavirus vaccination in girls and young women will decrease the need for surgical interventions on the cervix and can be expected to further reduce the risk of early birth. Together, this array of clinical interventions, each based on a substantial body of evidence, is likely to reduce rates of preterm birth and prevent death and disability in large numbers of children. The process begins with an acceptance that early birth is not an inevitable and natural feature of human reproduction. Preventative strategies are now available and need to be applied. The best outcomes may come from developing integrated strategies designed specifically for each health-care environment