José Alejandro Scolaro

Environmental adaptations in the retina of the Magellanic Penguin: Photoreceptors and outer plexiform layer

-The retina of the Magellanic Penguin (Spheniscus magellanicus) was studied with light and electron microscopy. Rods, double and single cones were observed. Rods showed a uniform density over the entire retina, whereas cones gradually decreased from center to periphery. Cone-to-rod ratio was 2.0 in the center and 1.1 at the margin of the retina. Rods had a large outer segment (26.6 ? 2.8 pm long, and 2.1 ? 0.4 pm wide). About 80% of the cones were double. Principal members had a yellowish-green oil droplet and their outer segment was larger than that of rods (27.2 ? 2.5 gtm, and 3.3 ? 0.6, tapering to 2.2 ? 0.3 pm wide). The accessory member had a short outer segment and was devoid of an oil droplet. Single cones had either a transparent or orange oil droplet and a very long and thin outer segment. The large size of rod and principal cone outer segments might be correlated with increased sensitivity of the retina, perhaps as an adaptation to low illumination levels in deep oceanic waters. Their large diameter also implies that image focusing in the Magellanic Penguin eye would not be very sharp. However, the structure of the outer plexiform layer suggests that the penguin retina would be adapted to the extreme changes in illumination and contrast conditions encountered by diving penguins. Received 20 September 1998, accepted 25 January 1999.

Reproductive strategies in males of the world's southernmost lizards.

Reproductive and life history patterns in reptiles are tightly related to the environmental conditions, so male reproductive cycles have been historically characterized as continuous, for tropical lizards, or seasonal, for temperate lizards. However, males of Liolaemus and Phymaturus lizards (Liolaemidae), from cold temperate climates of high altitudes or latitudes in Argentina and Chile, have developed a variety of reproductive cycles to coordinate with the short female reproductive season and to deal with the low frequency of reproductive females in the population. Using gonadal histology and morphological analysis, we describe the male reproductive biology, fat storage and sexual dimorphism of the viviparous lizards Liolaemus sarmientoi and Liolaemus magellanicus that inhabit an austral grass steppe at 51°S, in the southern limit of the American continent. Males of L. sarmientoi and L. magellanicus are reproductively available during the entire activity season of approximately 5 months. In addition, males of both species exhibit greater body sizes than females in morphological variables relevant in sexual selection. Meanwhile, females of both species exhibit larger inter-limb length than conspecific males, which suggests fecundity selection to increase space for a larger litter size. The continuous sperm production throughout the activity season allows these liolaemids to mate at any time when females ovulate, representing a selective advantage to deal with the short activity season and the adversities of the cold environment they inhabit.

DNA Barcoding of Phymaturus Lizards Reveals Conflicts in Species Delimitation within the patagonicus Clade

Abstract Under the DNA Barcode initiative, we used the mitochondrial locus cytochrome c oxidase I to test if this molecular marker would reliably distinguish among lizard species of the patagonicus clade of Phymaturus. Using 18 described species and two populations of unidentified species, we calculated intra- and interpopulation genetic distances for all operational taxonomic units and performed phylogenetic reconstructions using maximum parsimony and maximum likelihood. We identified different species that share the same barcode index number (BIN). We recorded only 12 of the 18 previously described species and one candidate species from the new population. By comparing our results with published morphological and molecular phylogenies, as well as with previous debates, we propose possible explanations for this. In some cases (such as the group with the same BIN formed by Phymaturus spurcus, Phymaturus spectabilis, Phymaturus excelsus, and Phymaturus agilis), where other authors debated the identity of the species, we suggest that the low genetic distances could be attributable to the presence of one species with high polymorphism. On the other hand, in geographically isolated species such as the group formed by Phymaturus payuniae and Phymaturus nevadoi, the group formed by Phymaturus somuncurensis and Phymaturus ceii, and the group formed by Phymaturus indistinctus and Phymaturus videlai, the topology of the phylogenetic trees indicates that the low genetic distances (also found by other authors analyzing cytochrome b) could be attributable to shared ancestral polymorphism resulting from incomplete lineage sorting.