Polymorphic microsatellite markers in the loggerhead shrike Lanius ludovicianus isolated from a library enriched for CA repeats.

Many species of true shrike (family Laniidae) are in decline world-wide, but the causes of the decline are in most cases poorly understood (Yosef & Lohrer 1995). Populations of at least two subspecies of the North American loggerhead shrike Lanius hfovicianus have suffered severe reductions this century: the San Clemente loggerhead shrike, L. 1. mearnsi, an endangered Californian Channel Island endemic, and L. 1. migrans on the east coast (Yosef & Lohrer 1995). We have developed microsatellite primers for the loggerhead shrike in order to study its mating system, population structure, migration patterns and genetic erosion of isolated populations. Such knowledge will be important in designing effective management programmes, and most of these primers should be immediately applicable to similar questions in other shrike species. A partial genomic library was constructed by digesting genomic DNA from a female loggerhead shrike (L. 1. mearnsi) with MboI, size-seleding (200-500 bp), and ligating into M13. Preliminary screens of the library with a (CAh, probe revealed large numbers of positive clones (about 1 in loo), which were al l found to be identical on sequencing and which contained an interrupted CA repeat. As an alternative strategy, a library enriched for CA repeats was constructed, using a modified version of the biotin capture method of Kandpal et al. (1994). Briefly, digested and size-selected genomic DNA was ligated to an MboI adaptor (Kandpal et at. 1994), and amplified in a PCR reaction using one of the MboI adaptor oligonucleotides as a primer, with the following cycle parameters: 1 x 94 "C, 3 min; 35 x 94 "C, 30 S, 55 "C, 30 S, 72 "C, 120 S; 1 x 72 "C, 10 min (as in Kandpal et al. 1994). The amplified inserts were denatured by boiling in a water bath for 10 min, and hybridization was carried out in a total volume of 100 pL containing 2-3 pg amplified insert, 1 pg of biotinylated(CA),, 0.5% SDS in 0.5 M sodium phosphate, pH 7.4, with