Myrmecological News 15 V-XXII Vienna, May 2011 Obituary Contributions by Ross Crozier on genetics and phylogeny of ants and other organisms Prof. Dr. Pekka Pamilo, Department of Biosciences, Box ogy, and he was supervised by William L. Brown Jr. He 65, 00014 University of Helsinki, Finland. completed his PhD in 1969 with a thesis entitled Genetic E-mail: [email protected] and phylogenetic studies on ants. The work was based on the best methods available at that time, karyotyping. While Myrmecol. News 15: V-XXII (online 24 June 2010) in Cornell, Ross was also supervised and influenced by one ISSN 1994-4136 (print), ISSN 1997-3500 (online) of the leading population geneticists, Bruce Wallace. Of Received 5 October 2010; accepted 6 October 2010 his teachers, Michael White had been influenced by J.B.S. Haldane at the University College London, and Bruce Wal- Abstract lace was a student of Theodosius Dobzhansky. We can thus In 1969, Ross Crozier completed his doctoral degree at Cornell see that his two academic grandfathers were central archi- University (USA). The title of his PhD thesis was Genetic and tects of the synthetic evolutionary theory. This was reflected phylogenetic studies on ants. During the following four decades in everything Ross did – he was always keen to under- he devoted his time to this same topic, and he also expanded his stand the genetic and evolutionary mechanisms and pro- research projects to include other social insects and many other cesses that underlie the patterns of current biodiversity. evolutionary questions. His active career came to a sudden and un- From Cornell Ross moved to Athens, University of Geor- expected stop when in November 2009 he died at his work place gia where he stayed until 1974. While continuing the work at the campus of James Cook University in Townsville (Austra- with ant karyotypes and chromosome polymorphisms, he lia). During the past 40 years he achieved a great deal scientifi- started to develop his research in new directions. A few cally, established and pioneered the research field of social in- years after receiving his PhD, Ross reviewed what was sect evolutionary genetics, and at the time of his death was still at known about hymenopteran chromosomes, largely based the peak of his scientific career. on his own work, in a book published in the series Animal Key words: Social insects, ants, genetics, evolution, karyotype, Cytogenetics (CROZIER 1975). In that book he discussed, in kin recognition, kin selection, caste determination, sex determi- addition to chromosomes, other important aspects of hy- nation, immune defense. menopteran reproductive systems and social life, and de- monstrated his ability to write excellent reviews, to sum- Early interests marize and synthesize information and to introduce new Rossiter (Ross) Crozier was born during the Second World ideas. Ross later continued cytogenetic research together War in India and he spent his childhood largely in South- with Hirotami Imai (see IMAI 2011), examining the evolu- East Asia where his father worked in various countries. Al- tionary processes of karyotype change in animals, not only ready during that time, at the age of five, he became fasci- ants but also vertebrates. His studies on ant chromosomes nated by social insects, when encouraged by his mother he revealed extreme variability in the chromosome numbers, cut open a termite nest with a kitchen knife and discovered with a haploid number ranging from 1 to 16 within the the wonderful society inside the nest. That fascination re- Myrmecia pilosula complex alone (CROSLAND & CROZIER mained throughout the rest of his life. He was sent to Gee- 1986). He worked with Imai on a minimum interaction the- long Grammar boarding school in Australia from where he ory, according to which selection favours karyotype rear- returned to the family in Asia for school holidays. This al- rangements which reduce deleterious chromosomal muta- lowed him to become familiar with the biodiversity on tions, and hence chromosome numbers are expected to in- both sides of the Wallace line, a factor which may have con- crease (IMAI & al. 1986). The conclusions from the Myr- tributed to his deep interest in studying and preserving bio- mecia species were consistent with the predictions of this diversity. theory as chromosome evolution of the complex seems to After finishing school, Ross considered a career as a have proceeded towards an increase in chromosome num- journalist but instead decided to start studying biology at ber by centric fission and inversions converting chromo- the University of Melbourne, where he graduated in 1966. somes from acro- to metacentrics (IMAI & al. 1994). His Master's thesis was supervised by his genetics teacher, Beginning of social insect evolutionary genetics the famous evolutionary cytogeneticist Michael J.D. White. The title of the thesis was Cytotaxonomic studies on Aus- It is fair to state that Ross was the person who established tralian Formicidae. The thesis made clear his two great in- the field of social insect evolutionary genetics or sociogen- terests: social insects (especially ants) and genetics. He had etics, largely during the 1970's. Based on his early-born actively collected ants during his school years and that in- and long-lasting interest in social insects, he focused his terest was now developing into a scientific career. His first scientific research on sociality. His formal training in gene- four scientific papers appeared in 1968, the first one in tics and evolutionary biology together with his intellect his CV was on chromosome staining techniques (CROZIER and curiosity made him ask questions on the evolution of 1968). sociality nobody had asked earlier. He also introduced For his doctoral studies, Ross moved to Cornell Univer- the theoretical framework of population genetics into res- sity, a central place for studies on ant systematics and biol- earch on social insects. This combination of research in- Ross H. Crozier Memorial Volume V terests quickly led to several important contributions. There BROWN (1968) who had proposed that odours function by were renowned geneticists working with social insects, marking strangers rather than by indicating nestmates. Some mainly bees (e.g., Warwick Kerr) but nobody interested in recent studies (GUERRIERI & al. 2009) favour Brown's pro- the ecological and evolutionary aspects in the same way posal. Nevertheless, CROZIER & DIX (1979) laid an impor- as Ross. He had the whole field open in front of him and he tant basis for conceptual studies of kin recognition and identified several important questions that should be ex- all studies on this topic are still built upon the basic models plored. His ability to identify essential questions and capa- and concepts that were developed in the 1970's. LACY & city to suggest useful approaches and solutions resembled SHERMAN (1983) further developed the models by introduc- the touch of the mythological king Midas – almost every ing the concepts of labels, templates and referents. Ross question Ross touched transferred into a new and flourish- later reviewed the rapidly expanding literature on kin re- ing line of research. cognition, both empirical and theoretical studies, in influ- Ross was undoubtedly one of the first to understand the ential papers (CROZIER 1987a, 1988, CROZIER & PAMILO importance of HAMILTON's (1964a, b) theory on social evo- 1996). His laboratory also conducted a series of empirical lution. He was, however, not satisfied with the way HA- studies on kin recognition in the ant genus Rhytidoponera MILTON (1964b) had presented the coefficients of genetic (e.g., PEETERS 1988, CROSLAND 1989a, b). relatedness for male haploid organisms. He pointed out Ross extended kin recognition models further to clonal (CROZIER 1970) that the relatedness of a haploid male to a invertebrates (CROZIER 1986) and introduced what is com- diploid female is not the same as the reverse relatedness monly known as Crozier's paradox (e.g., TSUTSUI & al. of a female to a male, and he also corrected a value pre- 2003, GARDNER & WEST 2009). Namely, in clonal orga- sented by Hamilton. Ross denoted his coefficients of re- nisms new mutations cannot ally with anyone else and are latedness with a symbol G, and these have later been called therefore selected against. It therefore becomes difficult to Crozier's coefficients (UYENOYAMA & FELDMAN 1981) or explain the maintenance of genetic diversity in such a sys- pedigree coefficients (CROZIER & PAMILO 1980). This was tem – thus a paradox. a very important contribution with regard to the central Another modeling exercise from the mid seventies was place of the concept of relatedness in kin selection and on colony-level selection (CROZIER & CONSUL 1976). Ross the later development of conflict models. It should be em- was always keen on the levels or units of selection, and he phasized that at the time when Ross published this note, approached the problem with great philosophical attitude Hamilton's work was not yet much appreciated and had in several reviews (CROZIER 1987b, 2008). The first theore- been cited altogether less than 20 times. tical model developed by CROZIER & CONSUL (1976) was Later Ross developed, together with his student Robin relatively simple, focusing on the conditions of maintaining Craig, a method for estimating relatedness from empirical genetic variation. At that time, mid 1970's, population gen- genotypic data (CRAIG & CROZIER 1979). The method was eticists had started to explore allozyme variation in natural based on a suggestion by ORLOVE (1975), and Craig & populations and discovered that populations harboured more Crozier applied it to estimate relatedness in the colonies genetic variation than had been anticipated. This observa- of the ant Myrmecia pilosula. It was later shown that this tion led to an active debate between the neutralist and selec- original method is statistically biased as it does not take tionist schools (see e.g., LEWONTIN 1974).