Siemann Liese A.

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Liese A.

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  • Article
    Vertical visual features have a strong influence on cuttlefish camouflage
    (Marine Biological Laboratory, 2013-04) Ulmer, Kevin M. ; Buresch, Kendra C. ; Kossodo, M. M. ; Mathger, Lydia M. ; Siemann, Liese A. ; Hanlon, Roger T.
    Cuttlefish and other cephalopods use visual cues from their surroundings to adaptively change their body pattern for camouflage. Numerous previous experiments have demonstrated the influence of two-dimensional (2D) substrates (e.g., sand and gravel habitats) on camouflage, yet many marine habitats have varied three-dimensional (3D) structures among which cuttlefish camouflage from predators, including benthic predators that view cuttlefish horizontally against such 3D backgrounds. We conducted laboratory experiments, using Sepia officinalis, to test the relative influence of horizontal versus vertical visual cues on cuttlefish camouflage: 2D patterns on benthic substrates were tested versus 2D wall patterns and 3D objects with patterns. Specifically, we investigated the influence of (i) quantity and (ii) placement of high-contrast elements on a 3D object or a 2D wall, as well as (iii) the diameter and (iv) number of 3D objects with high-contrast elements on cuttlefish body pattern expression. Additionally, we tested the influence of high-contrast visual stimuli covering the entire 2D benthic substrate versus the entire 2D wall. In all experiments, visual cues presented in the vertical plane evoked the strongest body pattern response in cuttlefish. These experiments support field observations that, in some marine habitats, cuttlefish will respond to vertically oriented background features even when the preponderance of visual information in their field of view seems to be from the 2D surrounding substrate. Such choices highlight the selective decision-making that occurs in cephalopods with their adaptive camouflage capability.
  • Thesis
    Mitochondrial DNA sequence variation in North Atlantic long-finned pilot whales, Globicephala melas
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1994-05) Siemann, Liese A.
    I sequenced mitochondrial DNA (mtDNA) from 59 long-finned pilot whales (Globicephala melas) that stranded on the coasts of Cape Cod, Newfoundland, Nova Scotia, Scotland, and England or were caught by commercial fisheries operating in the western North Atlantic, to determine if there is more than one genetic stock in the North Atlantic. Samples from 11 Atlantic and 2 Pacific short-finned pilot whales (G. macrorhynchus) and 11 bottlenose dolphins (Tursiops truncatus) were also analyzed. Sequences were obtained from 400-bp of the D-loop, a non-coding region involved in replication, and from 303-bp of the protein gene coding for cytochrome b. The D-loop sequences determined from 55 of the long-finned pilot whales were completely identical. Only the 2 sequences from Canadian whales showed some variability, differing from the other sequence by 0.25 - 0.50% (pairwise sequence divergence). All of the Atlantic short-finned pilot whales had identical D-loop sequences, and this sequence differed from the long-finned pilot whale sequences by 3.25 - 3.75%. The two Pacific short-finned pilot whale sequences differed from each other by 0.25%, from the Atlantic short-finned pilot whale sequence by 0.25 - 0.50%, and from the long-finned pilot whale sequences by 2.75 - 3.50%. D-loop nucleotide diversity in long-finned pilot whales was 0.03% and in short-finned pilot whales was 0.05%. The cytochrome b gene sequences determined for 16 long-finned pilot whales from all sampled locations, 4 Atlantic short-finned pilot whales, and two Pacific short finned pilot whales were all identical within each group, and differed from each other by 0.33 - 0.99%. Finally, D-loop sequences were also determined from 11 bottlenosed dolphins. All of the individuals had distinct D-loop sequences that differed by 0.25 - 4.25%, and the nucleotide diversity was 1.25%. Two dolphins were caught together, and the sequence divergence within this pair was 3.50%. These results suggest that long-finned pilot whales from the eastern and western North Atlantic are not genetically isolated from each other and that mtDNA variability in pilot whales may be unusually low. This might be a result of a slow rate of sequence evolution or metapopulation dynamics resulting from the social system of pilot whales. To examine the effect of social structure, I used an individual-based model designed to study the effect of sub-population extinction on mitochondrial genetic diversity in a pilot whale population which is subdivided as a result of this species' social system. MtDNA diversity was monitored in a population of pilot whales when extinction rates, mutation rates, and pod dynamics were altered. The results of the simulations indicate that if a pilot whale population experienced a moderate level of pod extinctions, it could undergo large fluctuations of mtDNA heterozygosity over time and frequently have the low heterozygosity observed in the North Atlantic pilot whale population.
  • Article
    Changeable camouflage : how well can flounder resemble the colour and spatial scale of substrates in their natural habitats?
    (Royal Society, 2017-03-08) Akkaynak, Derya ; Siemann, Liese A. ; Barbosa, Alexandra ; Mathger, Lydia M.
    Flounder change colour and pattern for camouflage. We used a spectrometer to measure reflectance spectra and a digital camera to capture body patterns of two flounder species camouflaged on four natural backgrounds of different spatial scale (sand, small gravel, large gravel and rocks). We quantified the degree of spectral match between flounder and background relative to the situation of perfect camouflage in which flounder and background were assumed to have identical spectral distribution. Computations were carried out for three biologically relevant observers: monochromatic squid, dichromatic crab and trichromatic guitarfish. Our computations present a new approach to analysing datasets with multiple spectra that have large variance. Furthermore, to investigate the spatial match between flounder and background, images of flounder patterns were analysed using a custom program originally developed to study cuttlefish camouflage. Our results show that all flounder and background spectra fall within the same colour gamut and that, in terms of different observer visual systems, flounder matched most substrates in luminance and colour contrast. Flounder matched the spatial scales of all substrates except for rocks. We discuss findings in terms of flounder biology; furthermore, we discuss our methodology in light of hyperspectral technologies that combine high-resolution spectral and spatial imaging.