Findings presented here for the chondrichthyans Prionace glauca and Isurus oxyrinchus show that the assembly of the spermatocyst and it\'s attached collecting duct are seamlessly connected developmental phenomena. The cyst\'s somatic cell component (i.e., Sertoli cells, SCs) and the duct\'s constituent cells derive both from a common precursor cell type (typically a large oblong cell) found among the A-spermatogonia in the folliculogenic region. Novel findings show that the co-developing collecting duct itself serves also as a source of either normal-looking or basophilic atypical SCs (aSCs), depending on whether the duct-cyst transition remains mitotically active and open, or is sealed. The aSCs arise from accumulating slender basophilic cells at the duct-cyst interface after which the newly formed cyst is sealed. Quantitative analysis of the latter in P. glauca revealed a correlation between the appearance of this aSC in immature cysts and the degenerated testicular condition that displays a gradient of multinucleate cell (MNC) death among spermatogonial cysts. Findings seem to implicate these aSCs in the life-death balance in mature spermatogonial cohorts downstream in the spermatogenic sequence, rather than in newly formed cysts that exhibit low rates of apoptosis. Photomicrographs of developing spermatogonial cysts showing several aSCs interspersed among cytoplasmically linked spermatogonia that are proliferating or have died, seem to suggest that these small SCs may be involved in confining MNC death to a given cyst region under conditions of subthreshold levels of apoptosis such as to ensure cyst recovery in immature spermatogonial cysts. Anat Rec, 301:1944-1954, 2018. © 2018 Wiley Periodicals, Inc.

Competition theory states that multiple species should not be able to occupy the same niche indefinitely. Morphologically, similar species are expected to be ecologically alike and exhibit little niche differentiation, which makes it difficult to explain the co-occurrence of cryptic species. Here, we investigated interspecific niche differentiation within a complex of cryptic bumblebee species that co-occur extensively in the United Kingdom. We compared the interspecific variation along different niche dimensions, to determine how they partition a niche to avoid competitive exclusion. We studied the species B. cryptarum, B. lucorum, and B. magnus at a single location in the northwest of Scotland throughout the flight season. Using mitochondrial DNA for species identification, we investigated differences in phenology, response to weather variables and forage use. We also estimated niche region and niche overlap between different castes of the three species. Our results show varying levels of niche partitioning between the bumblebee species along three niche dimensions. The species had contrasting phenologies: The phenology of B. magnus was delayed relative to the other two species, while B. cryptarum had a relatively extended phenology, with workers and males more common than B. lucorum early and late in the season. We found divergent thermal specialisation: In contrast to B. cryptarum and B. magnus, B. lucorum worker activity was skewed toward warmer, sunnier conditions, leading to interspecific temporal variation. Furthermore, the three species differentially exploited the available forage plants: In particular, unlike the other two species, B. magnus fed predominantly on species of heather. The results suggest that ecological divergence in different niche dimensions and spatio-temporal heterogeneity in the environment may contribute to the persistence of cryptic species in sympatry. Furthermore, our study suggests that cryptic species provide distinct and unique ecosystem services, demonstrating that morphological similarity does not necessarily equate to ecological equivalence.