ANNUAL AND LUNAR REPRODUCTIVE CYCLES IN LITTORINA SAXATILIS (OLIVI) AND DIFFERENCES BETWEEN BREEDING IN THE MARINE FIRTH OF FORTH AND THE FORTH ESTUARY

Gonads were most commonly reduced in October and fullest inMar-Jun with more pronounced seasonal differences in the estuarythan in the firth. Brood-pouches accordingly were fullest inspring-early summer and emptiest in autumn-early winter. Eggsand early embryos predominated in brood-pouches of early springbut were few in Aug-Oct whereas well-developed juveniles werefew in early spring, increased in spring-summer and came topredominate in Jun-Nov. Brood-pouch loads varied with size offemale but, for a standard 10 mm female, were significantlylower in the 2 estuarine sites than in the firth. Changes inmean brood-pouch count varied only 2.5-fold during the yearin the firth but 4.10-fold in the estuary. In vitro development of eggs to shelled juveniles with the velumresorbed took some 68 d at 10°C and 32%. Eggs and late brood-pouchjuveniles were significantly heavier in the estuary than inthe firth (dry weight, ash-free dry weight (AFDW), ash weight).AFDW changed little during development while ash weight (mostlyshell) increased 3.5-4.4-fold. In a laboratory tide tank, femalesreleased 60 d means of <1.3 juveniles d^–1; more inmid- and late year than in Jan-Mar, more from upshore firthfemales than from low shore or estuary females, more when heldat high tide-tank levels than at lower levels, and generallyat rates comparable to release in containers held at the siteof origin. Egg production in laboratory females did not keeppace with release of young and, at the end of trials, brood-pouchcounts were mostly lower than in contemporary free winkles.Females that had released most (e.g. at high tank levels) containedleast brood-pouch embryos and young subsequently. Release of young in the tide tank was markedly faster at timesnear new moon (often reaching or exceeding 2 female^–1d^–1) than near full moon (often <1 female^–1 d^–1).This lunar fluctuation was clearest in fast-releasing sets heldat high- or mid-tide tank levels. It was not observed in Jan-Mar(when release from most females was slow) nor in females atlow tank levels. (Received 3 September 1990; accepted 8 November 1990)     

The house mouse: a model and motor for evolutionary understanding

Commensal house mice have spread from their probable origin in north India, differentiating into a number of forms described variously as species, semispecies or subspecies. The different taxa can breed together and exchange genes but they retain their distinctiveness (although Mus ( musculus ) molossinus of Japan seems to be the result of a complete fusion between M.  ( m .)  musculus and M.  ( m .)  castaneus ). The most widespread form is M.  ( m. )  domesticus , which has successfully colonized every continent as a commensal, albeit with varying contributions from other Mus genomes. It has also been domesticated as the laboratory mouse. This means that the same genome is exposed to a wide variety of environments and gives tremendous opportunities for exploring the operation of different evolutionary mechanisms. Mice have accompanied evolutionary understanding from early Darwinian days – confirming Mendelian ratios and showing they applied in mammals, providing data on rates of evolution, and representing examples of dominance modification, differential survival, competition and other indicators of a struggle for existence. However, they have an unfulfilled potential to drive as well as to illuminate evolutionary theory – by revealing more about, for example, the interactions between gene flow and social determinants, constraints on introgression and physiological adjustments. This potential can be explored through our ever-deepening knowledge of the genome and molecular mechanisms, and by the application of new techniques, but its most effective agent will always be the cross-disciplinary synergy of visionary scientists like Julian Huxley, Charles Elton and Louis Thaler.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 335–347.     

Happy is the man that findeth wisdom

The hypothesis is suggested that resource depression is one important factor behind the observed regular nest spacing of many birds of prey. It predicts that the proportion of evasive prey in the predator's diet should be reflected in the degree of regularity in its nest spacing. The idea is tested on data from 24 raptorial bird populations of 19 species. The proportion of supposed evasive prey (birds and large mammals) in the diet was positively correlated with the degree of regularity in spacing of the nests, considering all populations or species. No such significant correlation was found for the six highly territorial species, whereas the correlation was highly significant for the other 13 species. Thus, the hypothesis seems most applicable to species with widely overlapping home ranges. However, resource depression could be one reason for territoriality.     

The significance of island biotas

Island biotas have played a significant part in evolutionary biology, because they are so often starkly different from continental biotas (even though it took Darwin some time to realize this; his visit to the Galapagos Islands was not the converting experience often claimed for it). In recent years, most interest has concentrated on species diversity on islands, but differentiation of endemics is probably worth more attention. Key factors in the evolution of island forms include the complementary processes of Mayr's 'genetic revolution' (a genetic bottleneck, particularly when a previously empty area is colonized; and adaptation in isolation), the opportunistic (not perfecting) nature of natural selection, and the ecological history of island colonists.     

Industrial melanism and peppered moths (Biston betularia (L.))

The spread of melanic forms of the peppered moth ( Biston betularia (L.)) over polluted areas of Britain from the mid-nineteenth century onwards, has become widely known and quoted as a classical example of microevolutionary change. Probably the most important factor in the spread (and subsequent decline, following the Clean Air Act) of the melanics has been bird predation on less cryptic individuals, but a range of other factors may also affect the maintenance of allele frequencies at any one place (site selection, dispersion, heterosis, frequency dependent selection, larval hardiness, etc). The development of the "Peppered Moth Story" is described, and suggestions made about needed research.     

The herbaceous lycophyte Haskinsia Grierson and Banks from the Devonian of western Venezuela, with observations on leaf morphology and fertile specimens

The Devonian herbaceous lycophyte genus Haskinsia Grierson and Banks is characterized by narrow dichotomizing stems and helically arranged petiolate leaves with a broad, approximately deltoid, lamina. New specimens are reported from four horizons in the Lower Member of the Campo Chico Formation, Sierra de Perijá, western Venezuela. H. sagittaka Edwards and Benedetto has sagittate leaves, and fertile specimens are reported for the first time; the ellipsoidal/obovoid adaxially-flattened sporangium is attached to unmodified leaves towards the top of the petiole in the adaxial position. H. sp. has sagittate leaves which are larger than any yet attributed to the genus but is represented by only three specimens. H. hastata sp. nov. has hastate leaves; the sporangia are more globose but positioned similarly to those of H. sagittata. The occurrence of the sporangia on unmodified microphylls indicates that Haskinsia is a member of Protolepidodendrales. The status of Haskinsiaceae is discussed. The Venezuelan specimens are compared with other records of Haskimi and Haskinsia -like plants from North America, Kazakhstan, North China, North Africa and Antarctica.