Biology subjects

Cullen, G.

Publications and source records attributed to Cullen, G..

3 recordsLinked to original sources

bioRxiv2025

Conservation relevant fine scale distribution and habitat associations of threatened elasmobranchs in temperate nearshore waters

Elasmobranchs are globally threatened and experiencing ongoing declines. Understanding threatened elasmobranch distribution is critical for developing effective marine conservation strategies. However, our knowledge of fine scale elasmobranch habitat association and distribution in temperate nearshore systems is limited. Here, we examined the presence, relative abundance and habitat association of sharks, skates and rays using benthic baited remote underwater stereo-video systems (SBRUVs). From 772 deployments (682 total hours, 53 minutes average soak time) across three years (2021-2023) and two Scottish sea lochs and adjacent bays, elasmobranchs were detected on 31.2% of deployments (n = 241). Our surveys detected six species of elasmobranchs, representing 17.6% of the resident elasmobranch diversity reported to date in nearshore waters < 200 m depth in UK waters. The species detected include two species listed as globally Vulnerable on the IUCN Red List, spiny dogfish (Squalus acanthias) and porbeagle (Lamna nasus) and one Critically Endangered species, flapper skate (Dipturus intermedius). Critically Endangered flapper skate were detected in 5.2% deployments (n = 40) and were the only species recorded which did not show a relationship between the probability of presence and substratum type. Our findings provide critical data on the fine scale spatial distribution and habitat use of elasmobranchs, informing evidence-based conservation measures and supporting more consistent and targeted policy action for these species in Scotland.

ecology↗

bioRxiv2024

Development of Germline Progenitors in Larval Queen Honeybee ovaries.

Honeybees (Apis mellifera) are a keystone species for managed pollination and the production of hive products. Eusociality in honeybees leads to much of the reproduction in a hive driven by the queen. Queen bees have two large active ovaries that can produce large numbers of eggs if conditions are appropriate. These ovaries are also active throughout the long lives of these insects, up to 5 years in some cases. Recent studies have indicated that the germline precursors of the adult honeybee queen ovary are organized into 8 cell clusters, joined together by a polyfusome; a cytoplasmic bridge. To understand the origin of these clusters, and trace the development of the honeybee queen ovary, we examined the cell types and regionalization of the developing larval and pupal queen ovaries. We used established (nanos and castor), and novel (odd skipped) gene expression markers to determine regions of the developing ovary. Primordial germline cells develop in the honeybee embryo and are organized into ovary structures before the embryo hatches. The ovary is regionalized by Larval Stage 3 into terminal filaments and germaria. At this stage clusters of germline cells in the germaria are joined by fusomes and are dividing synchronously. The origin of the 8-cell clusters in the adult germarium is therefore during larval stages. On emergence, the queen ovary has terminal filaments and germaria but has not yet developed any vitellaria, which are produced after the queen embarks on a nuptial flight. The lack of germaria, and the storing of germline progenitors as clusters, may be adaptions for queen bees to endure the metabolic demands of a nuptial flight, as well as rapidly lay large numbers of eggs to establish a hive.

developmental biology↗

bioRxiv2022

Germ-stem cells and oocyte production in the Honeybee Queen Ovary

Understanding the reproduction of honeybee queens is crucial to support populations of this economically important insect. Here we examine the structure of the honeybee ovary to determine the nature of the germ-stem cells in the ovary. Using a panel of marker genes that mark somatic or germ-line tissue in other insects we determine which cells in the honeybee ovary are somatic and which germline. We examine patterns of cell division, and demonstrate that, unlike Drosophila, there are no single germ-line stem cells that provide the germ-line in honeybees. Germ-line stem cells are clustered in groups of 8 cells, joined by a polyfusome, and collections of these, in each ovariole, maintain the germ-line during reproduction. We also show that these 8-cell clusters can divide, and that their division occurs such that the numbers of germ-line stem cells are relatively constant over the reproductive life of queen honeybees. This information helps us to understand the diversity of structures in insects reproduction, and provide information to better support honeybee reproduction.

developmental biology↗