In biology, a cline is a measurable gradient in a single character of a species across its geographical range. First coined by Julian Huxley in 1938, the “character” of the cline referred to is genetic, or phenotypic. Clines can show smooth, continuous gradation in a character, or they may show more abrupt changes in the trait from one geographic region to the next. A cline refers to a spatial gradient in a specific, singular trait, rather than a gradient in a population as a whole. A single population can therefore theoretically have as many clines. Additionally, Huxley recognised that these multiple independent clines may not act in concordance with each other. For example, it has been observed that in Australia, birds become smaller the further towards the north of the country they are found. In contrast, the intensity of their plumage colouration follows a different geographical trajectory, being most vibrant where humidity is highest and becoming less vibrant further into the arid centre of the country.
Because of this, clines were defined by Huxley as being an “auxiliary taxonomic principle”. While the terms “ecotype” and “cline” are sometimes used interchangeably, they do in fact differ in that “ecotype” refers to a population which differs from other populations in a number of characters, rather than the single character that varies amongst populations in a cline. Clines are cited to be the result of two opposing drivers: selection and gene flow. Selection causes adaptation to the local environment, resulting in different genotypes or phenotypes being favoured in different environments; this diversifying force is countered by gene flow, which has a homogenising effect on populations and prevents speciation through causing genetic admixture and blurring any distinct genetic boundaries. Clines are thought to arise under one of two conditions: “primary differentiation”, or “secondary contact”. Clines produced through this way are generated by spatial heterogeneity in environmental conditions.
The mechanism of selection acting upon organisms is therefore external. Species ranges span environmental gradients and, according to natural selection, different environments will favour different genotypes or phenotypes. In this way, when genetically or phenotypically uniform populations spread into novel environments, they will evolve to be uniquely adapted to the local environment, in the process creating a gradient in a genotypic or phenotypic trait; such clines in characters can not be maintained through selection alone if lots of gene flow occurred between populations, as this would tend to swamp out the effects of local adaptation. However, because species tend to have a limited dispersal range, restricted gene flow can serve as a type of barrier which encourages geographic differentiation. However, some degree of migration is required to maintain a cline. A classic example of the role of environmental gradients in creating clines is that of the peppered moth, Biston betularia, in the UK.
During the 19th century, when the industrial sector gained traction, coal emissions blackened vegetation across northwest England and parts of northern Wales. As a result of this, lighter morphs of the moth were more visible to predators against the blackened tree trunks and were therefore more predated relative to the darker morphs; the frequency of the more cryptic melanic morph of the peppered moth increased drastically in northern England. This cline in morph colour, from a dominance of lighter morphs in the west of England, to the higher frequency of melanic forms in the north, has been degrading since limitations to sooty emissions were introduced in the 1960s. Clines generated through this mechanism have arisen through the joining of two isolated populations which differentiated in allopatry, creating an intermediate zone; this secondary contact scenario may occur, for example, when climatic conditions change, allowing the ranges of populations to expand and meet. Because over time the effect of gene flow will tend to swamp out any regional differences and cause one large homogenous population, for a stable cline to be maintained when two populations join there must be a selective pressure maintaining a degree of differentiation between the two populations.
The mechanism of selection maintaining the clines in this scenario is intrinsic. This means that the fitness of individuals is independent of the external environment, selection is instead dependent on the genome of the individual. Intrinsic, or endogenous, selection can give rise to clines in characters though a variety of mechanisms. One way it may act is through heterozygote disadvantage, in which intermediate genotypes have a lower relative fitness than either homozygote genotypes; because of this disadvantage, one allele will tend to become fixed in a given population, such that populations will consist of either AA or aa individuals. The cline of heterozygotes, created when these respective populations come into contact is shaped by the
Tessa Duder is a New Zealand author of novels for young people, short stories and non-fiction, a former swimmer who won a silver medal for her country at the 1958 British Empire and Commonwealth Games. As a writer, she is known for her Alex quartet and long-term advocacy for New Zealand children's literature; as an editor she has published a number of anthologies. Duder was born Tessa Staveley in Auckland on 13 November 1940, the daughter of John Staveley, a doctor and pioneer of blood transfusion in New Zealand, knighted, Elvira Duder, a cellist, she was educated at the Diocesan School for Girls in Auckland, went on to study at Auckland University College in 1958 returned to the University of Auckland between 1982 and 1984. After leaving school, Staveley worked as a journalist for the Auckland Star from 1959 to 1964, before travelling to Europe and working for the Daily Express in London between 1964 and 1966, she married John Duder in 1964, the couple went on to have four daughters. Following the birth of her first child, Duder was a full-time mother for seven years, much of it spent in Pakistan.
She returned to Auckland in 1972. As a teenager, Staveley competed in the butterfly and medley swimming events, becoming a national record holder in both events during 1958–59, she won the New Zealand national 110 yards butterfly title in 1957 and 1958, the national individual medley championship in 1957, 1958, 1959. At the 1958 British Empire and Commonwealth Games in Cardiff, Staveley won the silver medal in the 110 yards butterfly, recording a time of 1:14.4 in the final. She was a member of the New Zealand women's 4 x 110 yards medley relay team, alongside Philippa Gould, Kay Sawyers, Jennifer Hunter, that finished in fourth place. Staveley was named New Zealand Swimmer of the Year in 1959. Duder began writing fiction in 1977, her first novel Night Race to Kawau was published by Oxford University Press in 1982. Her most successful works are the Alex quartet of novels which build upon her own childhood experiences by following a teenage competitive swimmer with Olympic ambitions; the series won three New Zealand Children's Book of three Esther Glen medals.
Alex has been translated into five languages and was for many years Penguin New Zealand's best selling work of fiction. A film production of Alex was commercially unsuccessful. Duder's work has been varied, including plays and biographies; the Tiggie Tompson Show won the 2000 New Zealand Post Senior Fiction Award for young adult fiction. Her first work for adults, a short story collection Is She Still Alive? reached number two on New Zealand bestseller lists in 2008. Duder has performed in several of her own plays and acted in 11 episodes of the New Zealand soap Shortland Street, she is a past president of the NZ Society of Authors. In 1990, Duder was awarded the New Zealand 1990 Commemoration Medal, she was appointed an Officer of the Order of the British Empire in the 1994 New Year Honours, for services to literature, has been awarded the Storylines Margaret Mahy Medal. She is a trustee of the Storylines Children's Literature Charitable Trust of New Zealand, the Spirit of Adventure Trust which operates the tall ship Spirit of New Zealand and the Operating Theatre Trust.
In 1991, she was the University of Waikato's first writer-in-residence. In 2003, she won the Katherine Mansfield fellowship to work for a year in Menton, in 2007 she travelled to Antarctica under the Artists to Antarctica programme, she was awarded an honorary doctorate by the University of Waikato in 2009. In 2013, she participated in the first Tall Ships Regatta from Sydney to Auckland, sailing aboard Spirit of New Zealand for the eight-day race crossing from Sydney to Opua. Duder lives on Auckland's North Shore. Novels for young people: Night Race to Kawau Jellybean Alex Alex in Winter Alessandra - Alex in Rome Songs for Alex Mercury Beach The Tiggie Tompson Show Hot Mail Tiggie Tompson, All at Sea Tiggie Tompson's Longest Journey Short Stories for Adults. Plays: The Runaway - one-act play for young actors about Joan of Arc The Warrior Virgin Non-Fiction: Kawau - the Governor's Gift The Book of Auckland Spirit of Adventure: the Story of New Zealand's sail training ship – with Captain Barry Thompson and Clifford Hawkins Waitemata - Auckland's Harbour of Sails Journey to Olympia - the story of the Ancient Olympics The Making of Alex: the movie In Search of Elisa Marchetti — a writer’s search for her Italian family Margaret Mahy - a writer's life The Word Witch - the magical verse of Margaret Mahy - The Story of Sir Peter Blake Official Site Works by or about Tessa Duder in libraries
HMNZS Charles Upham was a Mercandian 2-in-1 class roll-on/roll-off vessel operated by the Royal New Zealand Navy between 1994 and 2001. The vessel was built for the Danish shipping company Mercandia during the early 1980s, operated under the names Mercandian Queen II and Continental Queen II; the New Zealand Defence Force had identified the need for a logistic support ship as early as the 1970s but it was not until the 1991 white paper that planning to acquire a ship commenced in earnest. Mercandian Queen II was for sale around that time, although not as capable as the RNZN had specified, was purchased in 1994; the ship arrived in New Zealand in 1995 under the name Sealift, was commissioned that year as HMNZS Charles Upham, after the only combat soldier to be awarded the Victoria Cross twice, Captain Charles Upham. After some modification, the ship made two voyages to test her capabilities and determine what further work was required to make her operational. Significant problems with stability and seakeeping were encountered during the second voyage, the ship was removed from service on her return.
The cost of fixing the stability problems and fitting Charles Upham out for troop and vehicle transport was prohibitive, the work was postponed. In the meantime, the ship was chartered to Spanish company Contenemar SA in 1998 and used to transport citrus fruit around the Mediterranean. By 2001, the New Zealand government had decided that Charles Upham should be sold; the ship was sold to Contenemar converted into a vehicle carrier and onsold in 2009 to Indonesian company PT Pelayaran Putra Sejati. In the meantime, the RNZN sought to acquire a new logistic vessel, with HMNZS Canterbury entering service in 2007; the vessel was one of 137 cargo vessels built by Danish shipping company Mercandia between 1964 and 1996 for their worldwide shipping fleet. The ship is of the Mercandian 2-in-1 class design, with a displacement of 7,995 tonnes at light load, 10,500 tonnes at full load, she is 131.7 metres long, with a beam of 21.1 metres, a draught of 6.2 metres. The propulsion system consists of a MaK M 453AK diesel motor, which supplied 4,890 horsepower to a single controllable-pitch propeller.
This was supplemented by a bow thruster. Maximum speed was 14 knots, maximum range was 7,000 nautical miles at 15 knots; the ship had a two ramps for vehicle loading. She was designed to carry up to 7,000 tonnes of cargo; the crew complement was 17 strong, the ship was fitted with two I-band navigational radars. The vessel was built by Frederikshavns Værft in Denmark. Laid down as yard number 407, she was launched on 16 December 1983, completed on 6 April 1984; the vessel was assigned the IMO Number 8131128. The ship was built for and operated by Danish shipping company Mercandia, was flagged as a Danish vessel. During her initial civilian career, the vessel operated under the name Mercandian Queen II, except for a period during 1992 when she was named Continental Queen II; the RNZN began to identify the need for a logistic support ship in the 1970s. Such a ship would be used to support the defence and foreign policies of the New Zealand government in the South Pacific region by providing sealift for the New Zealand Army's Ready Reaction Force, with secondary roles including disaster relief, civil defence, Antarctic supply, United Nations operations.
The 1978 Defence Review noted the need for such a vessel, with attention drawn back to the acquisition of such a ship in the 1987 Defence White Paper. A 1988 study indicated that the minimum requirement was a vessel able to transport 200 soldiers and equipment, unload them either through beach landings or wharf facilities; the need for a transport vessel was again identified in the 1991 Defence White Paper, with such a vessel essential to meet the tasks specified for the New Zealand Defence Force in that document. A review subsequent to the 1991 White Paper proposed a less-capable vessel than with the ship able to perform wharf landings only; as well as the transportation of soldiers, the ship was envisaged for use during civil emergencies in South Pacific nations to deliver supplies of extract New Zealand citizens, to keep transport routes to New Zealand's offshore islands, or across Cook Strait, if civilian services became restricted or unavailable. The review concluded that the acquisition of a mid-size roll-on/roll-off vessel for use as a military sealift ship should be prioritised.
Union Rotorua was the first ship considered for acquisition, with inspection beginning in November 1991, but after the New Zealand Defence Force began to look at other vessels in mid-1992, Union Rotorua was dropped from contention. In researching New Zealand defence acquisitions, Peter Greener claims he can find no clear reason for Union Rotorua to be dropped, but identifies the size of the 205-metre ship, which would have been by far the largest vessel operated by the RNZN, the gas-turbine propulsion system, due for overhaul, as factors. Shipbroking company Rugg and Co was contracted in July 1992 to identify civilian ships that met the RNZN's criteria and were available to purchase second-hand.