Hazelton Peter D, Landis Andrew Gascho, McElwain Andrew, Olivencia Kyle, Carmignani Jason
D. B. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia, USA.
Department of Fisheries, Wildlife, and Environmental Science, State University of New York at Cobleskill, Cobleskill, New York, USA.
J Aquat Anim Health. 2024 Dec;36(4):310-320. doi: 10.1002/aah.10232. Epub 2024 Dec 1.
Freshwater mussels of the order Unionoida are among the most imperiled taxa in North America, and many species are undergoing enigmatic decline without fully understood causation. Disease pathology and parasitology have been identified as areas with significant knowledge gaps in relation to these declines. We investigated a shell deformity of unknown cause that is widespread in northeastern North America by adding to the clinical description from a mussel assemblage in Massachusetts with a deformity prevalence exceeding 50%. We build upon previous qualitative descriptions of this deformity with investigations of shell morphology and mussel age.
We conducted a qualitative survey of the mussel community to evaluate the prevalence of deformity. Mussels were classified as deformed based on the presence of a distinct truncation of the posterior margin of the shell. For the eastern elliptio Elliptio complanata, we evaluated the shell height, shell length, and height : length ratio of animals classified as deformed versus normal and we conducted a comparison to a reference population. We also incorporated shell thin sectioning and aging to qualitatively describe the deformity in cross section and to compare age distributions between deformed and normal eastern elliptio.
We observed the presence of this deformity in four species, including the eastern elliptio, eastern lampmussel Lampsilis radiata, eastern pearlshell Margaritifera margaritifera, and creeper Strophitus undulatus. In cross section, the deformity appeared to be caused by repeated disturbance in growth in the posterior portion of the shell. Deformed eastern elliptio had markedly shorter shells for a given shell height when compared to normal and reference mussels, and they tended to be older at shorter shell lengths than normal mussels from the same site.
The cause of the shell deformity in the United States remains unknown, although it appears similar in description to the deformity caused by a commensal midge, Xenochironomus canterburyensis, which infects a distantly related freshwater mussel in New Zealand. We highlight potential causes and the need for further investigation.
蚌目淡水贻贝是北美最濒危的生物分类群之一，许多物种正经历着神秘的衰退，其衰退原因尚未完全明确。疾病病理学和寄生虫学被认为是与这些衰退相关的知识存在重大空白的领域。我们通过补充马萨诸塞州一个贻贝群落的临床描述，对北美东北部广泛存在的一种病因不明的贝壳畸形进行了调查，该群落的畸形患病率超过50%。我们在先前对这种畸形的定性描述基础上，对贝壳形态和贻贝年龄进行了研究。
我们对贻贝群落进行了定性调查，以评估畸形的患病率。根据贝壳后缘是否有明显截断来将贻贝分类为畸形。对于东部椭圆蚌（Elliptio complanata），我们评估了被分类为畸形和正常的个体的壳高、壳长以及高长比，并与一个参考种群进行了比较。我们还进行了贝壳薄片切片和年龄测定，以定性描述畸形的横截面，并比较畸形和正常东部椭圆蚌的年龄分布。
我们在四种物种中观察到了这种畸形，包括东部椭圆蚌、东部灯蚌（Lampsilis radiata）、东部珍珠蚌（Margaritifera margaritifera）和匍匐蚌（Strophitus undulatus）。在横截面中，这种畸形似乎是由贝壳后部生长的反复干扰引起的。与正常和参考贻贝相比，畸形的东部椭圆蚌在给定壳高时壳明显更短，并且在相同壳长时，它们往往比来自同一地点的正常贻贝年龄更大。
美国贝壳畸形的原因仍然未知，尽管其描述似乎与一种共生蠓虫——坎特伯雷异摇蚊（Xenochironomus canterburyensis）引起的畸形相似，这种蠓虫感染新西兰一种亲缘关系较远的淡水贻贝。我们强调了潜在原因以及进一步调查的必要性。
