Relationships of Some Species of Digenea with the Marine Prosobranch Littorina littorea (L.) II. The Effect of Larval Digenea on the Reproductive Biology of L. littorea

1971 ◽  
Vol 45 (2-3) ◽  
pp. 145-159 ◽  
Author(s):  
E. M. Robson ◽  
I. C. Williams
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Sex Reversal ◽  
Littorina Littorea ◽  
Breeding Cycle ◽  
Reproductive Condition ◽  
Initial Infection ◽  
The North ◽  
Breeding Cycles ◽  
The Common

1. 5250 specimens of the common periwinkle, Littorina littorea (L.), from Scalby Rocks on the North Yorkshire coast were examined from October 1966 to November 1967 and data obtained on the size, sex and reproductive condition of the periwinkles and their infections with four species of Digenea, namely Cryptocotyle lingua (Creplin, 1825), Renicola roscovita (Stunkard, 1932), Himasthla leptosoma (Creplin, 1829) and Cercaria lebouri Stunkard, 1932.2. The normal breeding cycle of uninfected L. littorea and the breeding cycles found in periwinkles infected with larval Digenea are described and discussed. Initial infection takes place mainly when periwinkles are spent after their first breeding season and though later damage to the gonad may prevent reproduction, the breeding potential of the periwinkle population at Scalby Rocks is unlikely to be affected seriously. There was no evidence of sex reversal in uninfected or infected L. littorea and the normal sex ratio is 1:1. The phenomenon of gigantism as a result of digenean infection is discussed with respect to L. littorea.

Relationships of Some Species of Digenea with the Marine Prosobranch Littorina littorea (L.) I. The Occurrence of Larval Digenea in L, littorea on the North Yorkshire Coast

1970 ◽  
Vol 44 (2) ◽  
pp. 153-168 ◽  
Author(s):  
E. M. Robson ◽  
I. C. Williams
Keyword(s):  
Shell Length ◽  
Seasonal Changes ◽  
Littorina Littorea ◽  
Early Winter ◽  
The North ◽  
High Incidence ◽  
Unidentified Species ◽  
The Common

1. 8515 specimens of the common periwinkle, Littorina littorea (L.), from four localities on the North Yorkshire coast were examined for larval Digenea during 1966 and 1907. Four species were found, namely Cryptocotyle lingua (Creplin, 1825), Himasthla leptosoma (Creplin, 1829), Cercaria lebouri Stunkard, 1932 and Cercaria A, the incidence of infection with which correlated with the presence of sea bird and wader final hosts.2. 5878 of all L. littorea examined were from one locality of relatively high incidence of infection where there were seasonal changes in incidence, being greatest during the autumn and early winter and least during the summer. The incidence of infection was higher in larger than in smaller periwinkles except in infections with an unidentified species, named Cercaria A, where the incidence declined sharply in L. littorea above 25 mm shell length. The ecology of the infections is discussed.

scholarly journals Declines over the last two decades of five intertidal invertebrate species in the western North Atlantic

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Peter S. Petraitis ◽  
S. R. Dudgeon
Keyword(s):  
North Atlantic ◽  
Littorina Littorea ◽  
Rocky Shores ◽  
Nucella Lapillus ◽  
Important Food ◽  
Semibalanus Balanoides ◽  
Saturation State ◽  
Invertebrate Species ◽  
The North ◽  
The Common

Abstract Climate change has already altered the environmental conditions of the world’s oceans. Here we report declines in gastropod abundances and recruitment of mussels (Mytilus edulis) and barnacles (Semibalanus balanoides) over the last two decades that are correlated with changes in temperature and ocean conditions. Mussel recruitment is declining by 15.7% per year, barnacle recruitment by 5.0% per year, and abundances of three common gastropods are declining by an average of 3.1% per year (Testudinalia testudinalis, Littorina littorea, and Nucella lapillus). The declines in mussels and the common periwinkle (L. littorea) are correlated with warming sea temperatures and the declines in T. testudinalis and N. lapillus are correlated with aragonite saturation state, which affects rates of shell calcification. These species are common on shores throughout the North Atlantic and their loss is likely to lead to simplification of an important food web on rocky shores.

SEM and TEM observations of sperm development in the testis of the freshwater fish Oreochromis mossambicus

1990 ◽  
Vol 48 (3) ◽  
pp. 58-59
Author(s):  
Daryl A. Cornish ◽  
George L. Smit
Keyword(s):  
Morphological Characteristics ◽  
Oreochromis Mossambicus ◽  
Breeding Cycle ◽  
Limited Information ◽  
North West ◽  
The North ◽  
Sem And Tem ◽  
Sperm Development ◽  
Ultrastructural Characteristics ◽  
The University

Oreochromis mossambicus is currently receiving much attention as a candidater species for aquaculture programs within Southern Africa. This has stimulated interest in its breeding cycle as well as the morphological characteristics of the gonads. Limited information is available on SEM and TEM observations of the male gonads. It is known that the testis of O. mossambicus is a paired, intra-abdominal structure of the lobular type, although further details of its characteristics are not known. Current investigations have shown that spermatids reach full maturity some two months after the female becomes gravid. Throughout the year, the testes contain spermatids at various stages of development although spermiogenesis appears to be maximal during November when spawning occurs. This paper describes the morphological and ultrastructural characteristics of the testes and spermatids.Specimens of this fish were collected at Syferkuil Dam, 8 km north- west of the University of the North over a twelve month period, sacrificed and the testes excised.

scholarly journals Sex Ratios in a Warming World: Thermal Effects on Sex-Biased Survival, Sex Determination, and Sex Reversal

2021 ◽  
Vol 112 (2) ◽  
pp. 155-164
Author(s):  
Suzanne Edmands
Keyword(s):  
High Temperature ◽  
Sex Ratio ◽  
Sex Determination ◽  
Heat Tolerance ◽  
Sex Ratios ◽  
Sex Reversal ◽  
Survival Sex ◽  
Ratio Distortion ◽  
Warming World ◽  
Sex Ratio Distortion

Abstract Rising global temperatures threaten to disrupt population sex ratios, which can in turn cause mate shortages, reduce population growth and adaptive potential, and increase extinction risk, particularly when ratios are male biased. Sex ratio distortion can then have cascading effects across other species and even ecosystems. Our understanding of the problem is limited by how often studies measure temperature effects in both sexes. To address this, the current review surveyed 194 published studies of heat tolerance, finding that the majority did not even mention the sex of the individuals used, with <10% reporting results for males and females separately. Although the data are incomplete, this review assessed phylogenetic patterns of thermally induced sex ratio bias for 3 different mechanisms: sex-biased heat tolerance, temperature-dependent sex determination (TSD), and temperature-induced sex reversal. For sex-biased heat tolerance, documented examples span a large taxonomic range including arthropods, chordates, protists, and plants. Here, superior heat tolerance is more common in females than males, but the direction of tolerance appears to be phylogenetically fluid, perhaps due to the large number of contributing factors. For TSD, well-documented examples are limited to reptiles, where high temperature usually favors females, and fishes, where high temperature consistently favors males. For temperature-induced sex reversal, unambiguous cases are again limited to vertebrates, and high temperature usually favors males in fishes and amphibians, with mixed effects in reptiles. There is urgent need for further work on the full taxonomic extent of temperature-induced sex ratio distortion, including joint effects of the multiple contributing mechanisms.

Further Investigation upon the Water Movements in the English Channel. Drift-Bottle Experiments in the Summers of 1927, 1928 and 1929, with Critical Notes on Drift-Bottle Experiments in General.

1930 ◽  
Vol 17 (1) ◽  
pp. 241-275 ◽  
Author(s):  
J. N. Carruthers
Keyword(s):  
Wind Speed ◽  
North Sea ◽  
English Channel ◽  
The North ◽  
Different Types ◽  
The North Sea ◽  
The Common ◽  
Relationship Of ◽  
Great Simplicity ◽  
Simple Surface

In July–August of three different years common surface-floating bottles were set adrift at International Station E2 (49° 27' N.—4° 42' W.). With them, various types of drag-fitted bottles were also put out. The journeys accomplished are discussed, and the striking differences as between year and year in the case of the common surface floaters, and as between the different types in the same year, are commented upon in the light of the prevailing winds. An inter-relationship of great simplicity is deduced between wind speed and the rate of travel of simple surface floating bottles up-Channel and across the North Sea from the results of experiments carried out in four different summers.

Determinacy of fecundity in sole (Solea solea) from the Bristol Channel

1990 ◽  
Vol 70 (4) ◽  
pp. 803-813 ◽  
Author(s):  
J. W. Horwood ◽  
M. Greer Walker
Keyword(s):  
Bay Of Biscay ◽  
English Channel ◽  
Potential Fecundity ◽  
Frequency Distributions ◽  
The North ◽  
Size Frequency ◽  
Solea Solea ◽  
The North Sea ◽  
The Common ◽  
Common Sole

Ovaries of the common sole (Solea solea (Linnaeus)) were collected prior to, or at the beginning of, spawning from the spawning grounds in the Bristol Channel. Size frequency distributions of oocytes over 100 μm are presented. They clearly show a break in the size frequency distributions, at about 170 μm, indicating that the production of new oocytes to be spawned that season had ceased. It indicates that the sole is a determinate spawner and that, at least for this population, an annual potential fecundity can be measured. Estimated annual fecundity at length of Bristol Channel sole is calculated, and values are compared with those found for sole from the North Sea, eastern English Channel and the Bay of Biscay.

scholarly journals On tho proportions of the prevailing winds, the mean temperature, and depth of rain in the climate of London, computed through a cycle of Eighteen Years, or periods of the Moon’s declination

1843 ◽  
Vol 4 ◽  
pp. 300-300
Keyword(s):  
The Moon ◽  
Fair Weather ◽  
North West ◽  
West Wind ◽  
North East ◽  
East Wind ◽  
The North ◽  
The Common ◽  
The Mean ◽  
Solar Influence

In this paper the author investigates the periodical variations of the winds, rain and temperature, corresponding to the conditions of the moon’s declination, in a manner similar to that he has already followed in the case of the barometrical variations, on a period of years extending from 1815 to 1832 inclusive. In each case he gives tables of the average quantities for each week, at the middle of which the moon is in the equator, or else has either attained its maximum north or south declination. He thus finds that a north-east wind is most promoted by the constant solar influence which causes it, when the moon is about the equator, going from north to south; that a south-east wind, in like manner, prevails most when the moon is proceeding to acquire a southern declination ; that winds from the south and west blow more when the moon is in her mean degrees of declination, going either way, than with a full north or south declination ; and that a north-west wind, the common summer and fair weather wind of the climate, affects, in like manner, the mean declination, in either direction, in preference to the north or south, and most when the moon is coming north. He finds the average annual depth of rain, falling in the neighbourhood of London, is 25’17 inches.

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