Function and Causation of Social Signals in Lizards

SYNOPSIS. We describe here a multidisciplinary investigationof the stimuli and mechanisms controlling reproduction in thegreen anole lizard, Anolis carolinensis. Bothenvironmental andsocial stimuli that vary seasonally are used as proximate cuesto reproduction. In order for these ecological factors to initiatebreeding, they must be perceived and integrated in the centralnervous system. External and internal stimuli converge uponthe hypothalamus, the major neuroendocrine integrative areaof the brain, which, in turn, directly regulates pituitary andautonomic function. In addition to their role in reproduction,the gonadal hormones are important throughout the life of theorganism, acting both peripherally and centrally, to adapt theindividual to its environment. Thus, the environment, behavior,and physiology interact in complex ways to synchronize the socialand reproductive activities of individuals.     

Ammonoid growth rhythms

Determination of ammonite growth rate and longevity is an intriguing but difficult problem. Doguzhaeva (1982) made an exciting contribution through her study of 'growth rings' and their distribution on a variety of ammonite shells. She postulated a fortnightly or lunar monthly periodicity for chamber formation and a daily periodicity for growth line secretion on the outer shell. Before these suppositions become doctrine, however, a measure of skepticism seems warranted. Some of the relevant remarks run over familiar ground and were raised in response to Kahn & Pompea (1978), who assumed that growth increments on the outer shell of Nautilus are daily and septal deposition lunar monthly. Criticisms of their work focused on the nature of their data and the lack of a basis for the initial time assumptions (Jones & Thompson 1979; Saunders & Ward 1979). These criticisms apply to Doguzhaeva's study because her approach is similar and because Nautilus is the best living analog for ammonite growth.     

Analysis of a Carboniferous embryonic ammonoid assemblage implications for ammonoid embryology

An embryonic ammonoid assemblage was discovered in a carbonate concretion recovered from a dysoxic, relatively offshore marine shale of Virgilian (Upper Pennsylvanian) age in Kansas, USA. The assemblage consists primarily of two species of the Goniatitina, Aristocerassp. and Vidrioceras sp., whose initial chambers (protoconchs) differ in size and shape. Microscopic observations of serial thin sections of specimens at different growth stages reveal the sequence of embryonic shell development starting with the formation of the initial chamber and ending with the synchronous secretion of a prismatic proseptum and nacreous swelliig (primary varix) at the aperture. The mode of occurrence of the embryonic shells of the two species in the concretion suggests that these ammonoids produced numerous small offspring, a reproductive strategy similar to that in many extant coleoids. □ Ammonoids, embryonic shells, development, Carboniferous, Kansas.     

Nautilus—a poor model for the function and behavior of ammonoids?

Inferences drawn from the biology, function, and behavior of closely related living forms facilitate interpretation of the mode of life of groups known only from the fossil record. The choice of phylogenetically relevant modern 'model organisms' can have critical bearing on the resulting interpretations. The biology and behavior of fossil ammonoids are often interpreted in the light of evidence derived from the study of modern Nautilus . However, examination of the fossil record and cladistic analyses both indicate that coleoids are much more closely related to ammonoids than is Nautilus . Coleoid biology and behavior differ dramatically from the biology and behavior of Nautilus . Thus, the inclusion of coleoids as examples, rather than reliance on Nautilus alone, produces a strikingly different vision of ammonoid biology and suggests that inferences of ammonoid biology and behavior that rely exclusively on Nautilus should be reviewed. Two features related to swimming ability in Nautilus , static stability and large retractor muscles, are much reduced in many ammonoids, leading to the interpretation that ammonoids were poorer swimmers than Nautilus . However, reexamination of the evidence indicates that static stability should not play a role in the swimming of ammonoids with long body chambers. In addition, functional arguments suggest that a coleoid-like swimming mechanism should have evolved prior to the loss of the body chamber in coleoids. Thus, a coleoid-like swimming mechanism is likely to have evolved prior to the separation of ammonoid and coleoid lineages. A mechanism is proposed by which a coleoid swimming mechanism, independent of retractor muscle size, could function in ammonoids with long body chambers.□ Ammonoids, ammonites, evolution, functional morphology , Nautilus, phylogeny .     

Waterlogging duration: Interspecific comparison of Leptospermum scoparium (Forst et Forst.f.), Acacia melanoxylon (R. Br.), Nothofagus cunninghamii (Hook.) and Eucalyptus obliqua (L’Herit)

Abstract The effect of the duration of waterlogging on the pre‐dawn water potential, gas exchange, biomass accumulation and survival was investigated on four species, Leptospermum scoparium (Forst et Forst.f.), Acacia melanoxylon (R. Br.), Eucalyptus obliqua (L’Herit) and Nothofagus cunninghamii (Hook.). These species co‐occur, but are restricted to particular microsites. The three waterlogging treatments applied to potted seedlings were: four cycles of 15 days, two cycles of 30 days or one 60‐day cycle, followed by an equal period in freely drained conditions. Water potential, gas exchange, biomass accumulation and survival were not significantly affected by the duration of waterlogging in L. scoparium or A. melanoxylon. With increased waterlogging duration, N. cunninghamii had progressively decreased survival, had less biomass accumulation in all waterlogging treatments and more negative water potential after the 60‐day waterlogging cycle. In contrast, E. obliqua had low survival under the 15‐day waterlogging cycle treatment, although survival, biomass accumulation and maximum net photosynthesis were decreased by all waterlogging cycle treatments. Water potential was significantly lower (more negative) in E. obliqua than other species after the 30‐ and 60‐day waterlogging cycle treatments only. When exposed to oxygen deficit in hypoxic nutrient culture for 5 days, L. scoparium had 100% survival and maximum net photosynthesis was not affected. Acacia melanoxylon had 80% survival and decreased photosynthesis from 2 days of exposure onwards. Nothofagus cunninghamii and E. obliqua had 70% and 30% survival, respectively, and their photosynthesis was significantly depressed after 1 day of exposure to hypoxic conditions. Relative tolerance of the species examined to waterlogging and hypoxia was consistent with adaptation to conditions of seasonal variation in water table height and soil oxygenation concentration observed at the microsites occupied by the respective species. The results indicate that duration of waterlogging may be a major determinant in the microsite distribution of the co‐occurring species investigated.     

Theoretical aspects concerning transmission of the parasite Skrjabingylus nasicola (Leukart 1842) to stoats and weasels, with a review of the literature

Skrjabingylus nasicola belongs to a genus of parasitic nematodes which invade members of the Mustelidae. Despite its widespread occurrence, little is known about the natural mechanisms of transmission. Certain inferences as to how transmission might occur are drawn from indirect sources, such as the behaviour of the nematode first stage larvae, and the severity of infections assessed by quantifying skull damage to the host species. The possibility that the parasite is transmitted in times of food shortage for the host is discussed in the light of previous work and knowledge of the ecology of mustelids.     

The Genomic Quality of Rye B Chromosomes

DNA preparations from rye plants containing 0 and 6B chromosomeswere very similar when assessed by analytical ultraoentrifugation,renaturation kinetics and thermal denaturation. There was asuggestion that B chromosome DNA was slightly richer in sequencesof high cytosine and guanine content than that of the A complement.In situ hybridization showed that the DNA of the rye B chromosomeswas not all highly repetitious. The DNA of these B chromosomesis therefore concluded to be representative of a broad spectrumof DNA similar to the normal genome from which it was presumablyderived.