沟眶象和臭椿沟眶象的生态位分离及其机制研究

Eucryptorrhynchus scrobiculatus and E. brandti are sympatric and closely related species, which both are highly host-specific to Ailanthus altissima (Mill.) Swingle. They mainly feed on and destroy the root and stem of A. altissima, respectively. The reason that they damage different parts of the same host is unknown. Taking temporal, spatial and trophic niche as research clues, and focusing on the separation of trophic niche, studies will be conducted as follows: (1) temporal, spatial and trophic niche breadth, overlap and the influencing factors of both insects are determined by field investigating; (2) Differences on secondary substances and nutrient substances between root and stem of A. altissima are analyzed by GC-MS; rearing two kinds of larvae by exchanging natural diet, then determining the state of growth and development of two insects and conducting comparative analysis between previous transcriptome and transcriptome under this treatment; categories, content and function of the microbial community in the gut of adult and larva of two weevils are analyzed by metagenome sequencing; types, content and activity of cellulase in the gut of adult and larva are measured by the methods of Coomassie brilliant blue G-250 and DNS. Based on these researches, the mechanism of nutrient niche separation of two species of insects will be revealed hopefully. (3) The importance of temporal, spatial and trophic niche separation is weighed on the basis of niche breadth and overlap. Thus, the project not only is expected to explain coexistence mechanism from the perspective of niche separation, but also provides scientific reference for evolutionary relationship of closely related species.

同域分布的近缘种——沟眶象和臭椿沟眶象常混合发生、共同为害单一寄主臭椿，主要以幼虫分别钻蛀危害其树根和树干。二者共同为害同一寄主但为害部位有明显区别的现象未得到解释。本项目拟以二者的生态位分离为线索，并以营养生态位分离为重点，拟开展以下研究：①野外调查明确二者的时间、空间和营养生态位的宽度、重叠程度及其影响因素。②室内GC-MS法分析臭椿根部和干部次生物质和营养物质的差别；调换天然饲料成分人工饲养两种象虫，对饲虫进行生长发育测定和转录组测序分析；宏基因组测序分析二者肠道微生物的种类及功能的差异；G-250染色法和DNS法测定二者肠道酶系种类、含量和活性；综合分析两种象虫的营养生态位分离机制。③依据生态位宽度和生态位重叠指数，权衡时间、空间和营养生态位分离的相对重要性。本项目试图从生态位分离角度解释两种近缘种——沟眶象和臭椿沟眶象的共存，将为探索近缘种的进化关系提供有益参考。

同域分布的近缘种——沟眶象和臭椿沟眶象常混合发生、共同为害单一寄主臭椿，主要以幼虫分别钻蛀为害其树根和树干。二者共同为害同一寄主但为害部位有明显区别的现象未得到解释。本次研究从时间生态位、空间生态位、营养生态位等角度开展研究，明确了沟眶象和臭椿沟眶象成虫在季节和昼夜时间尺度上不存在时间生态位分离现象。这两种象甲成虫每年都存在两个发生高峰期，沟眶象成虫的发生高峰期约为6月上旬和8月中旬，臭椿沟眶象成虫的发生高峰期约为5月下旬和7月中旬；在一天时间中的上午11点到下午15点是这两种象甲成虫种群数量最多的时间；气候条件的变化会影响到这两种象甲的发生期和种群数量。沟眶象和臭椿沟眶象成虫在小尺度——臭椿树的空间生态位上存在一定的分离现象，主要是在臭椿树的垂直高度分布上存在差异，水平方向不存在差异；沟眶象和臭椿沟眶象在大尺度——中国范围内的空间生态位上不存在分离现象，降水情况是影响这两种象虫分布的主要因素；沟眶象和臭椿沟眶象的幼虫在其空间生态位上存在完全的分离现象。明确了沟眶象和臭椿沟眶象成虫存在较大程度的营养生态位分离，两种象甲幼虫可能存在完全的营养生态位分离。沟眶象成虫趋向于取食一年生枝条、多年生枝条和复叶叶柄，臭椿沟眶象成虫趋向于取食树干。沟眶象幼虫完全取食臭椿树根，臭椿沟眶象幼虫完全取食臭椿木质部及韧皮部。另外，两种象甲幼虫取食根粉配制的食物和树干及韧皮部配制的食物都能完成生长发育；但是，幼虫的发育状态会受到影响。两种象甲幼虫取食正常食物后的化蛹时间要早于取食控制组的食物的化蛹时间，相同象甲幼虫取食不同食物其过冷却点和冰点等有发生变化。另外，取食不同食物的两种或同种象甲的差异基因表达数约为13000，远大于取食相同食物的差异基因表达数1305和3621。通过差异基因GO富集分析发现，取食不同饲料的沟眶象或者臭椿沟眶象幼虫的差异基因GO富集显著集中在半胱氨酸内肽酶活性、脂质转运蛋白活性和核糖体；取食相同饲料的沟眶象或者臭椿沟眶象幼虫的差异基因GO富集显著集中在胞外区和几丁质分解代谢过程。三个维度的生态位分离对沟眶象和臭椿沟眶象共存的作用大小依次为：营养生态位分离＞垂直空间生态位分离＞水平空间生态位分离＞时间生态位分离。.以上研究内容为进一步研究沟眶象和臭椿沟眶象生态位分离的机制和进化过程奠定了坚实的基础，并为防治技术的开发提供了理论依据。