Hugh Loxdale

Loxdale was born in Horley, Surrey, England, on 9 September 1950, the second eldest child of three sons and two daughters born to Phyllis Marjorie Loxdale, née Duke (1921–1970) and John David (‘Jack’) Loxdale (1916–1993). He was named Hugh by his mother in honour of her late brother, Major Hugh Victor Duke (1918–1944), MC & Bar of the Devonshire Regiment, killed on D-Day, 6 June 1944.[1] In the early 1950s, his parents moved to Hemel Hempstead in Hertfordshire where he grew up.

Jack Loxdale in 1940

Phyllis M. Duke in WAAF uniform, c. 1944

His mother was born at Lezayre on the Isle of Man and later served from 1941 to 1946 in the Women's Auxiliary Air Force (WAAFs) as a Morse operator in a Royal Australian Air Force Sunderland Squadron stationed at Mount Batten Base, Plymouth.[2] His father, a manufacturing optician born in Hampstead, London, joined the Royal Naval Volunteer Reserve (RNVR) at the outbreak of the Second World War in 1939, later serving in the Merchant Service and finally in Royal Navy motor torpedo boats (MTBs) patrolling the Channel at the end of the war.

Hugh Loxdale was educated at Corner Hall Secondary Modern Boys’ School, Hemel Hempstead, Hertfordshire, England from 1962 to 1967, and Apsley Grammar School, Hemel Hempstead (now Longdean School) from 1967 to 1969. On leaving school, he joined the Entomology Department at Rothamsted Experimental Station (now Rothamsted Research), in Harpenden, Hertfordshire, working in the Insect Survey, then run by L.R. (Roy) Taylor (1924–2007),[3] studying the demography of moths and aphids as part of the national light trap and 12.2-metre-high (40 ft) suction trap surveys, respectively.[4]

During his time at Oxford, Loxdale designed and development a continuous, circulatory NADH+-coupled enzyme ADP assay system which allowed for the first time accurate measurement of pico-mole quantities of ADP released from small bundles of glycerol-extracted fibres (c. 60μm diam.; c. 1.2 cm. long) during activation by threshold calcium ion concentration [Ca2+] and stretch activation of fibrillar insect flight muscle (IFM), or [Ca2+] activation of vertebrate skeletal muscle; meanwhile the mechanical performance of the fibres could be simultaneously measured by oscillating them at a range of frequencies and amplitudes[5][6]. From this, he was able to demonstrate that, contrary to theory, the tension cost (ratio of ATPase activity over tension) did not change markedly as a function of the level of activation, i.e. the ATPase versus tension relationships remained essentially constant.[7] It was thus concluded that the rate constant of detachment of myosin from actin during the acto-myosin cross bridge cycle was not, as hitherto assumed, more especially for fibrillar IFM, the rate-limiting step in determining contraction speed of the muscle. Indeed, he was able to demonstrate using ATP solutions buffered with phosphate ions, that the tension cost and mechanical performance could even be dissociated from one another. In light of these findings, Roger H. Abbott formulated a four-state cross bridge cycle as most adequately accounting for the phenomena observed.[8] In addition, using glycerol extracted rabbit psoas muscle fibres activated in the absence of threshold concentrations of calcium ions using reduced ionic strength, Loxdale was also able to demonstrate that magnesium ions are necessary to stabilize the troponin-tropomyosin regulatory system, i.e. maintain this in the non-activated condition.[9]

Apparatus for simultaneously monitoring the ATPase activity and mechanical properties of small bundles of insect flight muscle fibres

Close-up of same showing series of water cooled muscle fibre immersion baths and specially designed circular UV cuvette

Original recording of simultaneous monitoring of ATPase activity, tension and oscillatory properties of small bundles of Lethocerus flight muscle fibres upon dual calcium ion and stretch activation, c. 1977

In terms of his insect population genetics studies, Loxdale in collaboration with Cliff Brookes, was the first to demonstrate at Rothamsted, using single locus polymorphic allozyme markers, that as with birds, different aphid species had different migratory urges and abilities as a consequence of their innate migratory behaviours (a notion supported by wind tunnel experiments performed at the Imperial College Field Station at Silwood Park, Ascot, by Professor Jim Hardie and colleagues).[10][11] In comparative studies performed over many years, later involving polymorphic microsatellite markers and a range of aphid species (Hemiptera: Aphididae), both pest and non-pest, it was revealed that some species such as the grain aphid, Sitobion avenae (F.), a predominantly asexual pest of cereals in Europe and elsewhere, did indeed appear capable of travelling long distances[12][13] In contrast, other species like the closely related blackberry-grain aphid, S. fragariae (Walker), a host alternating species with an autumn-winter sexual life cycle phase (i.e. the sexual females, on mating, laying cold hardy eggs), only travelled mainly short distances, perhaps less than 30 km.[14] Other species still, including the host alternating damson-hop aphid Phorodon humuli (Schrank)[15] and two species of non-host alternating tansy-feeding aphid − Macrosiphoniella tanacetaria (Kaltenbach) and Metopeurum fuscoviride Stroyan − also showed local dispersal behaviours.[16] Such data has considerable relevance to efforts to control aphid pests, globally amongst the most serious insect pests of many cash crops, more especially due to their ability to transmit pathogenic plant viruses of various kinds.[17] This work has been extensively reviewed in various publications, e.g.[18][19]

Macrosiphoniella tanacetaria, a non ant associated tansy aphid. Note mixed colony with two colour polymorphic forms, brown and green

Metopeurum fuscoviride, an ant attended tansy aphid species, also here showing two colour forms, brown and green

Loxdale and colleagues were also the first to demonstrate from their studies conducted in Jena that in the tansy aphid M. fuscoviride parasitized by its specialist wasp parasitoid Lysiphlebus hirticornis Mackauer (Hymenoptera: Braconidae), as the local genetic variation of the aphid increased, so did that of its parasitoid. This suggested a fine-grained co-evolutionary tracking to be in operation.[20] Such a scenario is supportive of the Red Queen hypothesis,[21] whereby a host organism (here an aphid) is attempting to evolve away from its antagonist (here a parasitoid), which is meanwhile co-evolving in order to retain the ability to attack it, i.e. keep pace with it in an ecological-evolutionary sense. Loxdale, in collaboration with G.M. Tatchell at Rothamsted, were also the first to determine the insecticide resistance status (here conferred by carboxylesterases, i.e. R1, R2 and R3 genotypes) of the serious agricultural pest the peach-potato aphid, Myzus persicae (Sulzer) captured in the UK network of 12.2. m high suction traps.[22] This involved using pH-buffered glycerol solutions containing antibiotic and gel electrophoresis to identify the level of carboxylesterase gene expression of the individual genotypes (the result of amplification of the E4 and FE4 resistance genes involved)[23][24] From this work, the spatial and temporal dynamics of this important (and now highly cross-resistant) pest aphid could be followed, thereby leading to more rational and effective control measures in the field.

With moths, Loxdale and his then PhD student Ian R. Wynne, were able to show using polymorphic allozyme markers, that in local populations of the November moth Epirrita dilutata (Denis & Schiffermüller) (Lepidoptera: Geometridae) inhabiting fragmented woodlands within the agro-ecosystem of the Rothamsted estate (330 ha), little inter-population gene flow was found to occur, even at distances of only a few kilometres. From these findings, it was concluded that the moths, which seemingly displayed high levels of habitat fidelity, possessed an innate reluctance to fly over flat, cultivated farmland. This study, here on a model Lepidopteran species, emphasizes the importance and utility of such genetic markers, even at a very local geographic scale, in studies of natural insect populations, both for purpose of conservation or control.[25]

Loxdale has written a series of overviews, many with colleagues, especially Dr. G. Lushai, highlighting the improbability of strict genetic uniformity in populations of clonal organisms such as aphids. This lack of uniformity is due to the rapid rate of mutation resulting from various mechanisms (e.g. point mutations due to errors of replication, inversion polymorphisms related to transposon effects, etc.) amplified by the huge reproductive potential of the animals concerned, e.g., not only do aphids show ‘telescoping of generations’ such that an adult asexual female has her children and grandchildren within her, but also display so-called ‘genetic inflation’, i.e. the production of a large number of asexual copies produced by a single female (10-100 offspring) in a short time (~ 10-14 days). Hence, a single aphid can, in theory (i.e. without mortality factors such as climate, predators, parasitoids and pathogens) produce enough offspring to cover the entire planet to a depth of many kilometres in a single growing season![26] This of course has serious potential consequences for the agricultural, horticultural and forestry industries worldwide.[27]

Aphids are known to show much variation − morphological, genetic, behavioural, etc. − which emphasizes the fact that they need to evolve quickly in the face of continuously developing ecological-evolutionary pressures and selective regimes (like the use of new kinds of insecticides), and hence need to be highly adaptive, rather than ecologically stagnant, i.e. living as large-scale clonal copies spread over wide geographic areas and persisting for long periods of time. Although some aphids such as M. persicae do show some insecticide resistant genotypes of this type,[28] these are maintained within the cultivated and manicured agro-ecosystem, hardly the real world in a long-term ecological sense.

In relation to theory, Loxdale & Lushai proposed in 2007 that the sexual cycle of aphids, rather than obligate asexuality, might be due to the necessity of telomere re-setting of the end of the chromosomes.[29][30] ["A telomere is a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes."; see Wikipedia for further details]. If such telomere re-setting does not occur, then, as the authors posit, the asexual lineages will become non-adaptive and die out as a function of transgenerational telomere shortening, a so-called aphid clone being, in effect, some kind of transgenerational entity, persisting (or so it was earlier believed) genetically unchanged over many generations

Critics of this theory[31][32] point out that telomere length in aphids is not highly regulated as it is in vertebrates (especially mammals), may occur even in the parthenogenetic phase of reproduction, and apparently aphid species colonies kept in culture over very many asexual generations (accepting something like 20 asexual generations per annum) have long telomere lengths. However, as is known, aphids can produce sexual forms (males and sexual females = oviparae) from time to time, even on secondary herbaceous hosts, when environmental stimuli are favourable, i.e. reduced light and temperature. Thus, it is possible that unless culture conditions are strictly maintained, some cryptic sexual reproduction may continue and hence some telomere re-setting occasionally occur.

In empirical studies of aphid chromosomes Loxdale, Lushai and colleagues were also able to demonstrate using RAPD (random amplified polymorphic DNA) markers that in asexual lineages (= 'clones' sensu lato) of cereal aphids (S. avenae and the bird cherry-oat aphid, Rhopalosiphum padi (L.)) maintained under strict conditions of rearing hygiene (i.e. each lineage was founded from a single parthenogenetic adult female reared on individual barley leaves in separate net-covered glass tubes standing in water), intra-clonal, trans-morph (sexual vs. asexual, winged vs. wingless) genetic changes were seen to occur. These may relate to changes in the RAPD primer binding sites in turn due perhaps to transposon effects.[33][34] At the chromosome level, recent studies by Loxdale in collaboration with Professor G. Manicardi, Dr. V. Monti and colleagues have demonstrated the existence of intra-clonal, inter-embryo genetic variation in terms of chromosome karyotype within individuals, and within and between clones of M. persicae.[35] Studies with both RAPDs and AFLPs (amplified fragment length polymorphic DNA) have also shown that aphid clones display both somatic and germline mutational changes within a few generations.[36] Hence the aphid clone is a very dynamic entity[37], not an invariant one as hitherto believed.

Loxdale has also written overviews on several key areas of biological thought and research. These include the migration and dispersal of insects in relation to their genotype and habitat[38]; intra-clonal genetic variation[39]; rapid evolution in insect populations due to various genetic-ecological mechanisms[40]; population proteomics (with Dr David Biron, Prof. Frédéric Thomas and colleagues)[41]; and most recently, on the improbability of generalism in nature, with special reference to insects, work in collaboration with G. Lushai and Professor Jeffrey Harvey.[42][43] The consensus of these articles is that the act of filling a new ecological niche is of course the fundamental act of specialization for any new species or sub-specific population. Whilst some species may be polyphagous to varying degrees, which the authors define, nevertheless diet breadth tends to involve preference for certain prey items in predatory as well as herbaceous species. Generalism, if it exists, is highly dependent upon an animal's morphology-anatomy, genetics, physiology-biochemistry, and chemistry, especially chemical ecology. This in turn governs the behaviour of the animal concerned and restrains it in terms of its habitat choice and what it can eat. In this light, the age old ‘arms race’ of insect herbivores with plants has led to the plants evolving an armoury of secondary chemical defenses which cause, more often than not, specialisms in terms of host and indeed habitat on the part of the herbivore/s involved. Ultimately, even apparently highly polyphagous species such as the aphid M. persicae, said to attack plants in 40 families,[44] may be because of its highly specialised biochemistry-enzymology. Most aphids are highly specialised on one host or closely related hosts (often in the same genus/family)[45], probably due to biochemical constraints, and if so, perhaps what one is seeing in M. persicae is a unique specialization rather than generalization.[46]

The picture is also complicated by the recent discovery in many species, including M. persicae and other aphids, following the application of high-resolution molecular markers, of morphologically similar/identical cryptic species. The discovery and realization of such cryptic entities is essential for successful pest control, especially including use of natural control agents such as hymenopterous wasp parasitoids and predators, as well as for the conservation of rare and endangered species.[47]

In terms of Loxdale's proteomics studies with Biron and colleagues in France, these have shown that nematomorph worms parasitizing crickets and grasshoppers (Orthoptera) cause fundamental neurological changes in the brain of their hosts. This induces the host to seek water and effectively commit suicide by jumping into it, whereupon the adult worm exits the host and seeks a mate and the females so mated then lay eggs to complete the life cycle.[48]

Recently, Loxdale has published an overview on the decline of entomological studies, especially in the UK, as a result of cutbacks in government and other funding sources. This problem not only seriously impacts directly on the importance of such studies in the fields of agriculture, horticulture, forestry, medicinal, veterinary and conservation studies, but also on the membership of the learned societies supporting entomology and the careers of those seeking long-term employment in this vital discipline.[49]

Loxdale has written over 500 poems in a variety of styles over the last 50 years or so, mainly on natural history themes, often with a philosophical slant. His first poem, Dragonfly, was published whilst he was still at Apsley Grammar School (now Longdean) in the late 1960s. To date he has published ten volumes of his poetry (as below), including one for children, Zoooo[50], whilst many poems have been published in books and magazines, on the www and the BBC website (e.g. his poem Across this Land, an epic poem on the destruction of the English countryside as a result of overzealous road construction). Because the author is a scientist, he tends to embrace realism in his poetic endeavours, having a duty, as he feels, to tell ‘it as it is’, even about such beloved and iconic animals as cats and dogs.

Fascinating Felines (2002) ISBN 9780954334703

The Eternal Quest: A celebration of nature in poetry (2003) ISBN 9780954334710

Blue Skies in Tuscany (2003) ISBN 9780954334727

Bird Words: Poetic images of wild birds (2003) ISBN 9780954334734

The Jena Poems (2010) ISBN 9780955392894

Love and the Sea (2010) ISBN 9780955392887

Nevisian Days: Poetry from a Caribbean Isle (2011) ISBN 9781908241009

Bird of Paradise: Selected Poems, 1968-2011 (2011) ISBN 9781908241016

Zoooo…Living Poems for Children (2012) ISBN 9781908241139

Red Tulips, Selected Poems, 1999-2016 (2017) ISBN 9781908241511

Loxdale has been married for 27 years to Nicola von Mende, PhD, molecular nematologist and latterly, publisher of natural history books.

Entomology Department at Rothamsted, May 1971. Dr. C.G. Johnson, Head of Department, is 6th from left in the first row; L.R. (Roy) Taylor 7th from left in the second row, whilst Loxdale, then age 20, is on the far left in the back row

Loxdale, then age 18, with his home made Williams-design moth trap, Hemel Hempstead, 1968

Who’s Who, 2005 to present Who’s Who online, 2007 to present

Royal Entomological Society

Cardiff University School of Biosciences

Hugh Loxdale CV