Hutcheson H J, Oliver J H, Houck M A, Strauss R E
Institute of Arthorpodology and Parasitology, Georgia Southern University, Stateboro 30460, USA.
J Med Entomol. 1995 Nov;32(6):827-42. doi: 10.1093/jmedent/32.6.827.
A morphological study of postlarval stages of the blacklegged tick, Ixodes scapularis Say, was conducted to examine congruence between northern (formerly I. dammini Spielman, Clifford, Piesman & Corwin) and southern morphotypes. The character set totaled 17 for females, 25 for males, and 28 for nymphs. Populations from 6 geographic areas, F1 progeny from reciprocal crosses between I. scapularis from Massachusetts and Georgia, and I. pacificus Cooley & Kohls from California were measured. Characters, except cornua length in nymphs, were positively correlated with PC1, indicating it was a general-size eigenvector. Characters used previously by others to distinguish northern and southern forms had a highly positive allometric relationship to general size. In canonical variate analysis (CVA) of nymphs, canonical score 1 (CAN1) discriminated I. pacificus from all other groups, canonical score 2 (CAN2) discriminated the remaining groups in a pattern that correlated with latitude, and canonical score 3 (CAN3) separated the western (Minnesota and Missouri) from the eastern groups. Size-free CVA indicated that north-south discrimination was size dependent, but that variation between Missouri and all other groups was not size related. Mahalanobis distances between groups within stages were significant with the exception of the 2 groups of female progeny of reciprocal crosses (Massachusetts x Georgia). Analysis of variance and Student-Newman-Keuls tests revealed that each geographic population differed from all other groups in at least 1 nymphal character. Nymphs from northern areas (Minnesota, Massachusetts, Maryland) differed from those from southern areas (Missouri, North Carolina, Georgia) in characters associated with the basis capitulum (longer intercornua and interauricular distances, basis capituli, and hypostome internal files, larger auriculae, but shorter cornua). Western populations (Minnesota, Missouri) differed from eastern populations in idiosomal characters (broader scutum, larger coxae III and IV). Frequency polygons of characters with the greatest differences indicated that data are continuous and geographic variation is overlapping. Thus, the data support the previous contention of conspecificity of I. scapularis and I. dammini. I. scapularis appears to be a polytypic species with a widespread geographic distribution exhibiting north-south and east-west morphological clines in eastern North America.
对肩突硬蜱（Ixodes scapularis Say）幼虫后期阶段进行了形态学研究，以检验北部形态型（以前的达氏硬蜱Ixodes dammini Spielman、Clifford、Piesman和Corwin）与南部形态型之间的一致性。雌性的特征集共有17个，雄性有25个，若虫有28个。对来自6个地理区域的种群、马萨诸塞州和佐治亚州的肩突硬蜱之间相互杂交的F1后代以及来自加利福尼亚州的太平洋硬蜱（Ixodes pacificus Cooley & Kohls）进行了测量。除若虫的角突长度外，其他特征与主成分1呈正相关，表明它是一个总体大小的特征向量。其他人以前用于区分北部和南部形态的特征与总体大小具有高度正异速生长关系。在若虫的典型变量分析（CVA）中，典型分数1（CAN1）将太平洋硬蜱与所有其他组区分开来，典型分数2（CAN2）以与纬度相关的模式区分其余组，典型分数3（CAN3）将西部组（明尼苏达州和密苏里州）与东部组区分开来。无大小CVA表明，南北区分与大小有关，但密苏里州与所有其他组之间的差异与大小无关。各阶段内组间的马氏距离显著，除了两组相互杂交的雌性后代（马萨诸塞州×佐治亚州）。方差分析和Student-Newman-Keuls检验表明，每个地理种群在至少一个若虫特征上与所有其他组不同。北部地区（明尼苏达州、马萨诸塞州、马里兰州）的若虫在与假头基部相关的特征（角突间和耳间距离更长、假头基部、口下板内纵列、耳叶更大但角突更短）上与南部地区（密苏里州、北卡罗来纳州、佐治亚州）的若虫不同。西部种群（明尼苏达州、密苏里州）在虫体特征（盾板更宽、第三和第四基节更大）上与东部种群不同。差异最大的特征的频率多边形表明数据是连续的，地理变异是重叠的。因此，这些数据支持了以前关于肩突硬蜱和达氏硬蜱同种的观点。肩突硬蜱似乎是一个多型种，地理分布广泛，在北美东部呈现出南北和东西形态渐变群。
