On the Origin of Thymic Lymphocytes

In the leopard frog (Rana pipiens), thymic lymphocytes do notoriginate from blood-borne stem cells that migrate into thethymus anlage; rather they arise in situ from elements in thethymic rudiment itself. After thymic differentiation, the lymphocytes(or their descendants) leave the thymus and extensively seedthe peripheral lymphoid organs. Indeed, virtually all the lymphocytesin the spleen, kidney, and bone marrow are ontogenically derivedfrom thymic cells. In postmetamorphic life, the thymus representsan organ in which lymphopoiesis is genuinely self-sustaining.Throughout the juvenile life of the frog, there is no indicationof an inward afferent stream of cells entering the intact thymus.     

The Importance of the History of Science to the American Society of Zoologists

As the history of science has developed as a professional intellectualdiscipline, it has had and will continue to have an importantrole in defining science and its place in our culture. Suchdefinitions should be based on as much information as possible.Scientists can help supply some of this information throughparticipation in symposia on the history of science. In addition,scientists can learn much about the nature of their disciplineby becoming aware of the concepts of science which are derivedfrom the careful analysis of its history. Efforts should bemade to bring historians of science and scientists togetherfor their mutual benefit.     

Variation in active and passive resource inputs to experimental pools: mechanisms and possible consequences for food webs

1. Cross‐ecosystem movements of resources, including detritus, nutrients and living prey, can strongly influence food web dynamics in recipient habitats. Variation in resource inputs is thought to be driven by factors external to the recipient habitat (e.g. donor habitat productivity and boundary conditions). However, inputs of or by ‘active’ living resources may be strongly influenced by recipient habitat quality when organisms exhibit behavioural habitat selection when crossing ecosystem boundaries. 2. To examine whether behavioural responses to recipient habitat quality alter the relative inputs of ‘active’ living and ‘passive’ detrital resources to recipient food webs, we manipulated the presence of caged predatory fish and measured biomass, energy and organic content of inputs to outdoor experimental pools of adult aquatic insects, frog eggs, terrestrial plant matter and terrestrial arthropods. 3. Caged fish reduced the biomass, energy and organic matter donated to pools by tree frog eggs by ～70%, but did not alter insect colonisation or passive allochthonous inputs of terrestrial arthropods and plant material. Terrestrial plant matter and adult aquatic insects provided the most energy and organic matter inputs to the pools (40–50%), while terrestrial arthropods provided the least (7%). Inputs of frog egg were relatively small but varied considerably among pools and over time (3%, range = 0–20%). Absolute and proportional amounts varied by input type. 4. Aquatic predators can strongly affect the magnitude of active, but not passive, inputs and that the effect of recipient habitat quality on active inputs is variable. Furthermore, some active inputs (i.e. aquatic insect colonists) can provide similar amounts of energy and organic matter as passive inputs of terrestrial plant matter, which are well known to be important. Because inputs differ in quality and the trophic level they subsidise, proportional changes in input type could have strong effects on recipient food webs. 5. Cross‐ecosystem resource inputs have previously been characterised as donor‐controlled. However, control by the recipient food web could lead to greater feedback between resource flow and consumer dynamics than has been appreciated so far.     

Evaluating Basking-Habitat Deficiency in the Threatened Eastern Massasauga Rattlesnake

ABSTRACT Woody plant succession is hypothesized to threaten many reptile populations by reducing the amount of solar energy available for thermoregulation. Mitigation via vegetation management is often recommended; however, the need for such management practices rarely has been evaluated. We examined the need for basking-site enhancement for the eastern massasauga rattlesnake (Sistrurus c. catenatus; hereafter EMR) in New York, USA, where only 2 populations remain: one at an open-canopy site and another at a closed-canopy site. Microhabitat temperatures were substantially lower at the closed-canopy site, where EMRs selected the warmest available basking sites. Eastern massasauga rattlesnakes in the open-canopy population selected basking sites that afforded greater cryptic cover. We recommend experimental reduction of shrub cover to improve EMR basking habitat at the closed-canopy site. More generally, we caution that management efforts to reduce shrub cover for basking EMRs should maintain adequate cryptic cover.     

Estimating changes in mean population age using the death distributions of live‐captured medflies

1. A simple, low‐cost approach to estimating population ageing was introduced based on a modified version of the captive cohort method – a technique developed earlier (Carey et al., Aging Cell, 7 , 426–437, 2008) in which information on the remaining lifespans of live‐captured medflies of unknown age is used to estimate the overall population age structure. 2. To test this approach approximately 1200 medflies near Volos, Greece were live captured from daily sampling over a 3‐month field season. 3. This simplified method reported: (i) an extraordinary post‐capture longevity of wild medflies in early season (>200 days in longest lived); (ii) a decrease of 50–75 days in the mean longevity from early‐season to late‐season flies; (iii) seasonality of frailty as indicated by the shorter‐lived flies in late autumn; (iv) cessation of fly emergence in late season as indicated by the absence of long‐lived individuals (indicating newly emerged at capture) sampled in the autumn; and (v) increase in mean age from about 20 days in early season to approximately 60 days in late season. 4. The applications of this simplified captive cohort method are discussed, including its use in the analysis of insect vector populations, Drosophila ecology and ageing in the wild, demographic toxicology, and age bias in sampling.     

The Effects of Priming and Accelerated Ageing upon the Nucleic Acid Content of Leek Seeds and their Embryos

Using seed priming and accelerated ageing techniques, a singlelot of leek (Allium porrum) seeds was manipulated to producefour lots of seeds with different germination performance. Changesin content of the major nucleic acid species in whole seedsand embryos of two of these lots (primed and unprimed), weredetermined over the early stages of germination. The major effectof priming was an increased level of RNA species in the seedsand embryos, and this difference was maintained during germination.Comparison of nucleic acid levels in the dry seeds of thesetwo lots and two others (aged and aged then primed) indicatedthat there was no correlation with germination performance.Similar comparisons of the nucleic acid levels in the embryosof seeds imbibed for 1 d showed only a limited correlation betweenrRNA levels and germination performance. Analysis of these datasuggests that accelerated ageing has an adverse effect uponendosperm cells, which results in the degradation of their nucleicacids during priming. Furthermore, the viability of these agedseeds also falls during priming. The data also indicate thatratios of rRNA to DNA correlate with germination performanceof the four lots of seeds studied. It is proposed that sucha relationship is indicative of the efficiency of a primingtreatment, and may be useful in comparisons of naturally varyingseed lots. Key words: Leek, seed, germination, priming, nucleic acids     

Oviposition response of Simulium reptans (Diptera: Simuliidae) to the presence of conspecific eggs

Abstract.

• 1 The oviposition behaviour of Simulium reptans L. is described from two sites on the River Spey, Scotland. Female aggregations were observed immediately downstream of oviposition sites and were composed mainly of gravid flies (range 60–80%0) together with smaller numbers that were either freshly bloodfed (range 2–17%) or infected with mermithid nematodes (range 0–30%).
• 2 The time from landing on the oviposition sites to the onset of oviposition was recorded. The time in the presence of greater than 1-day-old eggs did not significantly differ from sites with no eggs present. However, the presence of freshly laid or I-day-old eggs significantly shortened the time to onset of oviposition. The cues that elicit oviposition are unknown but it is speculated that they may involve a pheromone.